//
//  GCDAsyncUdpSocket
//
//  This class is in the public domain.
//  Originally created by Robbie Hanson of Deusty LLC.
//  Updated and maintained by Deusty LLC and the Apple development community.
//
//  https://github.com/robbiehanson/CocoaAsyncSocket
//

#import "GCDAsyncUdpSocket.h"

#if ! __has_feature(objc_arc)
#warning This file must be compiled with ARC. Use -fobjc-arc flag (or convert project to ARC).
// For more information see: https://github.com/robbiehanson/CocoaAsyncSocket/wiki/ARC
#endif

#if TARGET_OS_IPHONE
#import <CFNetwork/CFNetwork.h>
#import <UIKit/UIKit.h>
#endif

#import <arpa/inet.h>
#import <fcntl.h>
#import <ifaddrs.h>
#import <netdb.h>
#import <net/if.h>
#import <sys/socket.h>
#import <sys/types.h>


#if 0

// Logging Enabled - See log level below

// Logging uses the CocoaLumberjack framework (which is also GCD based).
// http://code.google.com/p/cocoalumberjack/
//
// It allows us to do a lot of logging without significantly slowing down the code.
#import "DDLog.h"

#define LogAsync   NO
#define LogContext 65535

#define LogObjc(flg, frmt, ...) LOG_OBJC_MAYBE(LogAsync, logLevel, flg, LogContext, frmt, ##__VA_ARGS__)
#define LogC(flg, frmt, ...)    LOG_C_MAYBE(LogAsync, logLevel, flg, LogContext, frmt, ##__VA_ARGS__)

#define LogError(frmt, ...)     LogObjc(LOG_FLAG_ERROR,   (@"%@: " frmt), THIS_FILE, ##__VA_ARGS__)
#define LogWarn(frmt, ...)      LogObjc(LOG_FLAG_WARN,    (@"%@: " frmt), THIS_FILE, ##__VA_ARGS__)
#define LogInfo(frmt, ...)      LogObjc(LOG_FLAG_INFO,    (@"%@: " frmt), THIS_FILE, ##__VA_ARGS__)
#define LogVerbose(frmt, ...)   LogObjc(LOG_FLAG_VERBOSE, (@"%@: " frmt), THIS_FILE, ##__VA_ARGS__)

#define LogCError(frmt, ...)    LogC(LOG_FLAG_ERROR,   (@"%@: " frmt), THIS_FILE, ##__VA_ARGS__)
#define LogCWarn(frmt, ...)     LogC(LOG_FLAG_WARN,    (@"%@: " frmt), THIS_FILE, ##__VA_ARGS__)
#define LogCInfo(frmt, ...)     LogC(LOG_FLAG_INFO,    (@"%@: " frmt), THIS_FILE, ##__VA_ARGS__)
#define LogCVerbose(frmt, ...)  LogC(LOG_FLAG_VERBOSE, (@"%@: " frmt), THIS_FILE, ##__VA_ARGS__)

#define LogTrace()              LogObjc(LOG_FLAG_VERBOSE, @"%@: %@", THIS_FILE, THIS_METHOD)
#define LogCTrace()             LogC(LOG_FLAG_VERBOSE, @"%@: %s", THIS_FILE, __FUNCTION__)

// Log levels : off, error, warn, info, verbose
static const int logLevel = LOG_LEVEL_VERBOSE;

#else

// Logging Disabled

#define LogError(frmt, ...)     {}
#define LogWarn(frmt, ...)      {}
#define LogInfo(frmt, ...)      {}
#define LogVerbose(frmt, ...)   {}

#define LogCError(frmt, ...)    {}
#define LogCWarn(frmt, ...)     {}
#define LogCInfo(frmt, ...)     {}
#define LogCVerbose(frmt, ...)  {}

#define LogTrace()              {}
#define LogCTrace(frmt, ...)    {}

#endif

/**
 * Seeing a return statements within an inner block
 * can sometimes be mistaken for a return point of the enclosing method.
 * This makes inline blocks a bit easier to read.
 **/
#define return_from_block  return

/**
 * A socket file descriptor is really just an integer.
 * It represents the index of the socket within the kernel.
 * This makes invalid file descriptor comparisons easier to read.
 **/
#define SOCKET_NULL -1

/**
 * Just to type less code.
 **/
#define AutoreleasedBlock(block) ^{ @autoreleasepool { block(); }}


@class GCDAsyncUdpSendPacket;

NSString *const GCDAsyncUdpSocketException = @"GCDAsyncUdpSocketException";
NSString *const GCDAsyncUdpSocketErrorDomain = @"GCDAsyncUdpSocketErrorDomain";

NSString *const GCDAsyncUdpSocketQueueName = @"GCDAsyncUdpSocket";
NSString *const GCDAsyncUdpSocketThreadName = @"GCDAsyncUdpSocket-CFStream";

enum GCDAsyncUdpSocketFlags
{
    kDidCreateSockets        = 1 <<  0,  // If set, the sockets have been created.
    kDidBind                 = 1 <<  1,  // If set, bind has been called.
    kConnecting              = 1 <<  2,  // If set, a connection attempt is in progress.
    kDidConnect              = 1 <<  3,  // If set, socket is connected.
    kReceiveOnce             = 1 <<  4,  // If set, one-at-a-time receive is enabled
    kReceiveContinuous       = 1 <<  5,  // If set, continuous receive is enabled
    kIPv4Deactivated         = 1 <<  6,  // If set, socket4 was closed due to bind or connect on IPv6.
    kIPv6Deactivated         = 1 <<  7,  // If set, socket6 was closed due to bind or connect on IPv4.
    kSend4SourceSuspended    = 1 <<  8,  // If set, send4Source is suspended.
    kSend6SourceSuspended    = 1 <<  9,  // If set, send6Source is suspended.
    kReceive4SourceSuspended = 1 << 10,  // If set, receive4Source is suspended.
    kReceive6SourceSuspended = 1 << 11,  // If set, receive6Source is suspended.
    kSock4CanAcceptBytes     = 1 << 12,  // If set, we know socket4 can accept bytes. If unset, it's unknown.
    kSock6CanAcceptBytes     = 1 << 13,  // If set, we know socket6 can accept bytes. If unset, it's unknown.
    kForbidSendReceive       = 1 << 14,  // If set, no new send or receive operations are allowed to be queued.
    kCloseAfterSends         = 1 << 15,  // If set, close as soon as no more sends are queued.
    kFlipFlop                = 1 << 16,  // Used to alternate between IPv4 and IPv6 sockets.
#if TARGET_OS_IPHONE
    kAddedStreamListener     = 1 << 17,  // If set, CFStreams have been added to listener thread
#endif
};

enum GCDAsyncUdpSocketConfig
{
    kIPv4Disabled  = 1 << 0,  // If set, IPv4 is disabled
    kIPv6Disabled  = 1 << 1,  // If set, IPv6 is disabled
    kPreferIPv4    = 1 << 2,  // If set, IPv4 is preferred over IPv6
    kPreferIPv6    = 1 << 3,  // If set, IPv6 is preferred over IPv4
};

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark -
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

@interface GCDAsyncUdpSocket ()
{
#if __has_feature(objc_arc_weak)
    __weak id delegate;
#else
    __unsafe_unretained id delegate;
#endif
    dispatch_queue_t delegateQueue;
    
    GCDAsyncUdpSocketReceiveFilterBlock receiveFilterBlock;
    dispatch_queue_t receiveFilterQueue;
    BOOL receiveFilterAsync;
    
    GCDAsyncUdpSocketSendFilterBlock sendFilterBlock;
    dispatch_queue_t sendFilterQueue;
    BOOL sendFilterAsync;
    
    uint32_t flags;
    uint16_t config;
    
    uint16_t max4ReceiveSize;
    uint32_t max6ReceiveSize;
    
    int socket4FD;
    int socket6FD;
    
    dispatch_queue_t socketQueue;
    
    dispatch_source_t send4Source;
    dispatch_source_t send6Source;
    dispatch_source_t receive4Source;
    dispatch_source_t receive6Source;
    dispatch_source_t sendTimer;
    
    GCDAsyncUdpSendPacket *currentSend;
    NSMutableArray *sendQueue;
    
    unsigned long socket4FDBytesAvailable;
    unsigned long socket6FDBytesAvailable;
    
    uint32_t pendingFilterOperations;
    
    NSData   *cachedLocalAddress4;
    NSString *cachedLocalHost4;
    uint16_t  cachedLocalPort4;
    
    NSData   *cachedLocalAddress6;
    NSString *cachedLocalHost6;
    uint16_t  cachedLocalPort6;
    
    NSData   *cachedConnectedAddress;
    NSString *cachedConnectedHost;
    uint16_t  cachedConnectedPort;
    int       cachedConnectedFamily;
    
    void *IsOnSocketQueueOrTargetQueueKey;
    
#if TARGET_OS_IPHONE
    CFStreamClientContext streamContext;
    CFReadStreamRef readStream4;
    CFReadStreamRef readStream6;
    CFWriteStreamRef writeStream4;
    CFWriteStreamRef writeStream6;
#endif
    
    id userData;
}

- (void)resumeSend4Source;
- (void)resumeSend6Source;
- (void)resumeReceive4Source;
- (void)resumeReceive6Source;
- (void)closeSockets;

- (void)maybeConnect;
- (BOOL)connectWithAddress4:(NSData *)address4 error:(NSError **)errPtr;
- (BOOL)connectWithAddress6:(NSData *)address6 error:(NSError **)errPtr;

- (void)maybeDequeueSend;
- (void)doPreSend;
- (void)doSend;
- (void)endCurrentSend;
- (void)setupSendTimerWithTimeout:(NSTimeInterval)timeout;

- (void)doReceive;
- (void)doReceiveEOF;

- (void)closeWithError:(NSError *)error;

- (BOOL)performMulticastRequest:(int)requestType forGroup:(NSString *)group onInterface:(NSString *)interface error:(NSError **)errPtr;

#if TARGET_OS_IPHONE
- (BOOL)createReadAndWriteStreams:(NSError **)errPtr;
- (BOOL)registerForStreamCallbacks:(NSError **)errPtr;
- (BOOL)addStreamsToRunLoop:(NSError **)errPtr;
- (BOOL)openStreams:(NSError **)errPtr;
- (void)removeStreamsFromRunLoop;
- (void)closeReadAndWriteStreams;
#endif

+ (NSString *)hostFromSockaddr4:(const struct sockaddr_in *)pSockaddr4;
+ (NSString *)hostFromSockaddr6:(const struct sockaddr_in6 *)pSockaddr6;
+ (uint16_t)portFromSockaddr4:(const struct sockaddr_in *)pSockaddr4;
+ (uint16_t)portFromSockaddr6:(const struct sockaddr_in6 *)pSockaddr6;

#if TARGET_OS_IPHONE
// Forward declaration
+ (void)listenerThread;
#endif

@end

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark -
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

/**
 * The GCDAsyncUdpSendPacket encompasses the instructions for a single send/write.
 **/
@interface GCDAsyncUdpSendPacket : NSObject {
@public
    NSData *buffer;
    NSTimeInterval timeout;
    long tag;
    
    BOOL resolveInProgress;
    BOOL filterInProgress;
    
    NSArray *resolvedAddresses;
    NSError *resolveError;
    
    NSData *address;
    int addressFamily;
}

- (id)initWithData:(NSData *)d timeout:(NSTimeInterval)t tag:(long)i;

@end

@implementation GCDAsyncUdpSendPacket

- (id)initWithData:(NSData *)d timeout:(NSTimeInterval)t tag:(long)i
{
    if ((self = [super init]))
    {
        buffer = d;
        timeout = t;
        tag = i;
        
        resolveInProgress = NO;
    }
    return self;
}


@end

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark -
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

@interface GCDAsyncUdpSpecialPacket : NSObject {
@public
    //	uint8_t type;
    
    BOOL resolveInProgress;
    
    NSArray *addresses;
    NSError *error;
}

- (id)init;

@end

@implementation GCDAsyncUdpSpecialPacket

- (id)init
{
    self = [super init];
    return self;
}


@end

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark -
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

@implementation GCDAsyncUdpSocket

- (id)init
{
    LogTrace();
    
    return [self initWithDelegate:nil delegateQueue:NULL socketQueue:NULL];
}

- (id)initWithSocketQueue:(dispatch_queue_t)sq
{
    LogTrace();
    
    return [self initWithDelegate:nil delegateQueue:NULL socketQueue:sq];
}

- (id)initWithDelegate:(id <GCDAsyncUdpSocketDelegate>)aDelegate delegateQueue:(dispatch_queue_t)dq
{
    LogTrace();
    
    return [self initWithDelegate:aDelegate delegateQueue:dq socketQueue:NULL];
}

- (id)initWithDelegate:(id <GCDAsyncUdpSocketDelegate>)aDelegate delegateQueue:(dispatch_queue_t)dq socketQueue:(dispatch_queue_t)sq
{
    LogTrace();
    
    if ((self = [super init]))
    {
        delegate = aDelegate;
        
        if (dq)
        {
            delegateQueue = dq;
#if !OS_OBJECT_USE_OBJC
            dispatch_retain(delegateQueue);
#endif
        }
        
        max4ReceiveSize = 9216;
        max6ReceiveSize = 9216;
        
        socket4FD = SOCKET_NULL;
        socket6FD = SOCKET_NULL;
        
        if (sq)
        {
            NSAssert(sq != dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0),
                     @"The given socketQueue parameter must not be a concurrent queue.");
            NSAssert(sq != dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0),
                     @"The given socketQueue parameter must not be a concurrent queue.");
            NSAssert(sq != dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),
                     @"The given socketQueue parameter must not be a concurrent queue.");
            
            socketQueue = sq;
#if !OS_OBJECT_USE_OBJC
            dispatch_retain(socketQueue);
#endif
        }
        else
        {
            socketQueue = dispatch_queue_create([GCDAsyncUdpSocketQueueName UTF8String], NULL);
        }
        
        // The dispatch_queue_set_specific() and dispatch_get_specific() functions take a "void *key" parameter.
        // From the documentation:
        //
        // > Keys are only compared as pointers and are never dereferenced.
        // > Thus, you can use a pointer to a static variable for a specific subsystem or
        // > any other value that allows you to identify the value uniquely.
        //
        // We're just going to use the memory address of an ivar.
        // Specifically an ivar that is explicitly named for our purpose to make the code more readable.
        //
        // However, it feels tedious (and less readable) to include the "&" all the time:
        // dispatch_get_specific(&IsOnSocketQueueOrTargetQueueKey)
        //
        // So we're going to make it so it doesn't matter if we use the '&' or not,
        // by assigning the value of the ivar to the address of the ivar.
        // Thus: IsOnSocketQueueOrTargetQueueKey == &IsOnSocketQueueOrTargetQueueKey;
        
        IsOnSocketQueueOrTargetQueueKey = &IsOnSocketQueueOrTargetQueueKey;
        
        void *nonNullUnusedPointer = (__bridge void *)self;
        dispatch_queue_set_specific(socketQueue, IsOnSocketQueueOrTargetQueueKey, nonNullUnusedPointer, NULL);
        
        currentSend = nil;
        sendQueue = [[NSMutableArray alloc] initWithCapacity:5];
        
#if TARGET_OS_IPHONE
        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(applicationWillEnterForeground:)
                                                     name:UIApplicationWillEnterForegroundNotification
                                                   object:nil];
#endif
    }
    return self;
}

- (void)dealloc
{
    LogInfo(@"%@ - %@ (start)", THIS_METHOD, self);
    
#if TARGET_OS_IPHONE
    [[NSNotificationCenter defaultCenter] removeObserver:self];
#endif
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
    {
        [self closeWithError:nil];
    }
    else
    {
        dispatch_sync(socketQueue, ^{
            [self closeWithError:nil];
        });
    }
    
    delegate = nil;
#if !OS_OBJECT_USE_OBJC
    if (delegateQueue) dispatch_release(delegateQueue);
#endif
    delegateQueue = NULL;
    
#if !OS_OBJECT_USE_OBJC
    if (socketQueue) dispatch_release(socketQueue);
#endif
    socketQueue = NULL;
    
    LogInfo(@"%@ - %@ (finish)", THIS_METHOD, self);
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Configuration
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

- (id)delegate
{
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
    {
        return delegate;
    }
    else
    {
        __block id result = nil;
        
        dispatch_sync(socketQueue, ^{
            result = delegate;
        });
        
        return result;
    }
}

- (void)setDelegate:(id <GCDAsyncUdpSocketDelegate>)newDelegate synchronously:(BOOL)synchronously
{
    dispatch_block_t block = ^{
        delegate = newDelegate;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey)) {
        block();
    }
    else {
        if (synchronously)
            dispatch_sync(socketQueue, block);
        else
            dispatch_async(socketQueue, block);
    }
}

- (void)setDelegate:(id <GCDAsyncUdpSocketDelegate>)newDelegate
{
    [self setDelegate:newDelegate synchronously:NO];
}

- (void)synchronouslySetDelegate:(id <GCDAsyncUdpSocketDelegate>)newDelegate
{
    [self setDelegate:newDelegate synchronously:YES];
}

- (dispatch_queue_t)delegateQueue
{
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
    {
        return delegateQueue;
    }
    else
    {
        __block dispatch_queue_t result = NULL;
        
        dispatch_sync(socketQueue, ^{
            result = delegateQueue;
        });
        
        return result;
    }
}

- (void)setDelegateQueue:(dispatch_queue_t)newDelegateQueue synchronously:(BOOL)synchronously
{
    dispatch_block_t block = ^{
        
#if !OS_OBJECT_USE_OBJC
        if (delegateQueue) dispatch_release(delegateQueue);
        if (newDelegateQueue) dispatch_retain(newDelegateQueue);
#endif
        
        delegateQueue = newDelegateQueue;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey)) {
        block();
    }
    else {
        if (synchronously)
            dispatch_sync(socketQueue, block);
        else
            dispatch_async(socketQueue, block);
    }
}

- (void)setDelegateQueue:(dispatch_queue_t)newDelegateQueue
{
    [self setDelegateQueue:newDelegateQueue synchronously:NO];
}

- (void)synchronouslySetDelegateQueue:(dispatch_queue_t)newDelegateQueue
{
    [self setDelegateQueue:newDelegateQueue synchronously:YES];
}

- (void)getDelegate:(id <GCDAsyncUdpSocketDelegate> *)delegatePtr delegateQueue:(dispatch_queue_t *)delegateQueuePtr
{
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
    {
        if (delegatePtr) *delegatePtr = delegate;
        if (delegateQueuePtr) *delegateQueuePtr = delegateQueue;
    }
    else
    {
        __block id dPtr = NULL;
        __block dispatch_queue_t dqPtr = NULL;
        
        dispatch_sync(socketQueue, ^{
            dPtr = delegate;
            dqPtr = delegateQueue;
        });
        
        if (delegatePtr) *delegatePtr = dPtr;
        if (delegateQueuePtr) *delegateQueuePtr = dqPtr;
    }
}

- (void)setDelegate:(id <GCDAsyncUdpSocketDelegate>)newDelegate delegateQueue:(dispatch_queue_t)newDelegateQueue synchronously:(BOOL)synchronously
{
    dispatch_block_t block = ^{
        
        delegate = newDelegate;
        
#if !OS_OBJECT_USE_OBJC
        if (delegateQueue) dispatch_release(delegateQueue);
        if (newDelegateQueue) dispatch_retain(newDelegateQueue);
#endif
        
        delegateQueue = newDelegateQueue;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey)) {
        block();
    }
    else {
        if (synchronously)
            dispatch_sync(socketQueue, block);
        else
            dispatch_async(socketQueue, block);
    }
}

- (void)setDelegate:(id <GCDAsyncUdpSocketDelegate>)newDelegate delegateQueue:(dispatch_queue_t)newDelegateQueue
{
    [self setDelegate:newDelegate delegateQueue:newDelegateQueue synchronously:NO];
}

- (void)synchronouslySetDelegate:(id <GCDAsyncUdpSocketDelegate>)newDelegate delegateQueue:(dispatch_queue_t)newDelegateQueue
{
    [self setDelegate:newDelegate delegateQueue:newDelegateQueue synchronously:YES];
}

- (BOOL)isIPv4Enabled
{
    // Note: YES means kIPv4Disabled is OFF
    
    __block BOOL result = NO;
    
    dispatch_block_t block = ^{
        
        result = ((config & kIPv4Disabled) == 0);
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    return result;
}

- (void)setIPv4Enabled:(BOOL)flag
{
    // Note: YES means kIPv4Disabled is OFF
    
    dispatch_block_t block = ^{
        
        LogVerbose(@"%@ %@", THIS_METHOD, (flag ? @"YES" : @"NO"));
        
        if (flag)
            config &= ~kIPv4Disabled;
        else
            config |= kIPv4Disabled;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_async(socketQueue, block);
}

- (BOOL)isIPv6Enabled
{
    // Note: YES means kIPv6Disabled is OFF
    
    __block BOOL result = NO;
    
    dispatch_block_t block = ^{
        
        result = ((config & kIPv6Disabled) == 0);
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    return result;
}

- (void)setIPv6Enabled:(BOOL)flag
{
    // Note: YES means kIPv6Disabled is OFF
    
    dispatch_block_t block = ^{
        
        LogVerbose(@"%@ %@", THIS_METHOD, (flag ? @"YES" : @"NO"));
        
        if (flag)
            config &= ~kIPv6Disabled;
        else
            config |= kIPv6Disabled;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_async(socketQueue, block);
}

- (BOOL)isIPv4Preferred
{
    __block BOOL result = NO;
    
    dispatch_block_t block = ^{
        result = (config & kPreferIPv4) ? YES : NO;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    return result;
}

- (BOOL)isIPv6Preferred
{
    __block BOOL result = NO;
    
    dispatch_block_t block = ^{
        result = (config & kPreferIPv6) ? YES : NO;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    return result;
}

- (BOOL)isIPVersionNeutral
{
    __block BOOL result = NO;
    
    dispatch_block_t block = ^{
        result = (config & (kPreferIPv4 | kPreferIPv6)) == 0;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    return result;
}

- (void)setPreferIPv4
{
    dispatch_block_t block = ^{
        
        LogTrace();
        
        config |=  kPreferIPv4;
        config &= ~kPreferIPv6;
        
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_async(socketQueue, block);
}

- (void)setPreferIPv6
{
    dispatch_block_t block = ^{
        
        LogTrace();
        
        config &= ~kPreferIPv4;
        config |=  kPreferIPv6;
        
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_async(socketQueue, block);
}

- (void)setIPVersionNeutral
{
    dispatch_block_t block = ^{
        
        LogTrace();
        
        config &= ~kPreferIPv4;
        config &= ~kPreferIPv6;
        
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_async(socketQueue, block);
}

- (uint16_t)maxReceiveIPv4BufferSize
{
    __block uint16_t result = 0;
    
    dispatch_block_t block = ^{
        
        result = max4ReceiveSize;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    return result;
}

- (void)setMaxReceiveIPv4BufferSize:(uint16_t)max
{
    dispatch_block_t block = ^{
        
        LogVerbose(@"%@ %u", THIS_METHOD, (unsigned)max);
        
        max4ReceiveSize = max;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_async(socketQueue, block);
}

- (uint32_t)maxReceiveIPv6BufferSize
{
    __block uint32_t result = 0;
    
    dispatch_block_t block = ^{
        
        result = max6ReceiveSize;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    return result;
}

- (void)setMaxReceiveIPv6BufferSize:(uint32_t)max
{
    dispatch_block_t block = ^{
        
        LogVerbose(@"%@ %u", THIS_METHOD, (unsigned)max);
        
        max6ReceiveSize = max;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_async(socketQueue, block);
}


- (id)userData
{
    __block id result = nil;
    
    dispatch_block_t block = ^{
        
        result = userData;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    return result;
}

- (void)setUserData:(id)arbitraryUserData
{
    dispatch_block_t block = ^{
        
        if (userData != arbitraryUserData)
        {
            userData = arbitraryUserData;
        }
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_async(socketQueue, block);
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Delegate Helpers
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

- (void)notifyDidConnectToAddress:(NSData *)anAddress
{
    LogTrace();
    
    __strong id theDelegate = delegate;
    if (delegateQueue && [theDelegate respondsToSelector:@selector(udpSocket:didConnectToAddress:)])
    {
        NSData *address = [anAddress copy]; // In case param is NSMutableData
        
        dispatch_async(delegateQueue, ^{ @autoreleasepool {
            
            [theDelegate udpSocket:self didConnectToAddress:address];
        }});
    }
}

- (void)notifyDidNotConnect:(NSError *)error
{
    LogTrace();
    
    __strong id theDelegate = delegate;
    if (delegateQueue && [theDelegate respondsToSelector:@selector(udpSocket:didNotConnect:)])
    {
        dispatch_async(delegateQueue, ^{ @autoreleasepool {
            
            [theDelegate udpSocket:self didNotConnect:error];
        }});
    }
}

- (void)notifyDidSendDataWithTag:(long)tag
{
    LogTrace();
    
    __strong id theDelegate = delegate;
    if (delegateQueue && [theDelegate respondsToSelector:@selector(udpSocket:didSendDataWithTag:)])
    {
        dispatch_async(delegateQueue, ^{ @autoreleasepool {
            
            [theDelegate udpSocket:self didSendDataWithTag:tag];
        }});
    }
}

- (void)notifyDidNotSendDataWithTag:(long)tag dueToError:(NSError *)error
{
    LogTrace();
    
    __strong id theDelegate = delegate;
    if (delegateQueue && [theDelegate respondsToSelector:@selector(udpSocket:didNotSendDataWithTag:dueToError:)])
    {
        dispatch_async(delegateQueue, ^{ @autoreleasepool {
            
            [theDelegate udpSocket:self didNotSendDataWithTag:tag dueToError:error];
        }});
    }
}

- (void)notifyDidReceiveData:(NSData *)data fromAddress:(NSData *)address withFilterContext:(id)context
{
    LogTrace();
    
    SEL selector = @selector(udpSocket:didReceiveData:fromAddress:withFilterContext:);
    
    __strong id theDelegate = delegate;
    if (delegateQueue && [theDelegate respondsToSelector:selector])
    {
        dispatch_async(delegateQueue, ^{ @autoreleasepool {
            
            [theDelegate udpSocket:self didReceiveData:data fromAddress:address withFilterContext:context];
        }});
    }
}

- (void)notifyDidCloseWithError:(NSError *)error
{
    LogTrace();
    
    __strong id theDelegate = delegate;
    if (delegateQueue && [theDelegate respondsToSelector:@selector(udpSocketDidClose:withError:)])
    {
        dispatch_async(delegateQueue, ^{ @autoreleasepool {
            
            [theDelegate udpSocketDidClose:self withError:error];
        }});
    }
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Errors
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

- (NSError *)badConfigError:(NSString *)errMsg
{
    NSDictionary *userInfo = [NSDictionary dictionaryWithObject:errMsg forKey:NSLocalizedDescriptionKey];
    
    return [NSError errorWithDomain:GCDAsyncUdpSocketErrorDomain
                               code:GCDAsyncUdpSocketBadConfigError
                           userInfo:userInfo];
}

- (NSError *)badParamError:(NSString *)errMsg
{
    NSDictionary *userInfo = [NSDictionary dictionaryWithObject:errMsg forKey:NSLocalizedDescriptionKey];
    
    return [NSError errorWithDomain:GCDAsyncUdpSocketErrorDomain
                               code:GCDAsyncUdpSocketBadParamError
                           userInfo:userInfo];
}

- (NSError *)gaiError:(int)gai_error
{
    NSString *errMsg = [NSString stringWithCString:gai_strerror(gai_error) encoding:NSASCIIStringEncoding];
    NSDictionary *userInfo = [NSDictionary dictionaryWithObject:errMsg forKey:NSLocalizedDescriptionKey];
    
    return [NSError errorWithDomain:@"kCFStreamErrorDomainNetDB" code:gai_error userInfo:userInfo];
}

- (NSError *)errnoErrorWithReason:(NSString *)reason
{
    NSString *errMsg = [NSString stringWithUTF8String:strerror(errno)];
    NSDictionary *userInfo;
    
    if (reason)
        userInfo = [NSDictionary dictionaryWithObjectsAndKeys:errMsg, NSLocalizedDescriptionKey,
                    reason, NSLocalizedFailureReasonErrorKey, nil];
    else
        userInfo = [NSDictionary dictionaryWithObjectsAndKeys:errMsg, NSLocalizedDescriptionKey, nil];
    
    return [NSError errorWithDomain:NSPOSIXErrorDomain code:errno userInfo:userInfo];
}

- (NSError *)errnoError
{
    return [self errnoErrorWithReason:nil];
}

/**
 * Returns a standard send timeout error.
 **/
- (NSError *)sendTimeoutError
{
    NSString *errMsg = NSLocalizedStringWithDefaultValue(@"GCDAsyncUdpSocketSendTimeoutError",
                                                         @"GCDAsyncUdpSocket", [NSBundle mainBundle],
                                                         @"Send operation timed out", nil);
    
    NSDictionary *userInfo = [NSDictionary dictionaryWithObject:errMsg forKey:NSLocalizedDescriptionKey];
    
    return [NSError errorWithDomain:GCDAsyncUdpSocketErrorDomain
                               code:GCDAsyncUdpSocketSendTimeoutError
                           userInfo:userInfo];
}

- (NSError *)socketClosedError
{
    NSString *errMsg = NSLocalizedStringWithDefaultValue(@"GCDAsyncUdpSocketClosedError",
                                                         @"GCDAsyncUdpSocket", [NSBundle mainBundle],
                                                         @"Socket closed", nil);
    
    NSDictionary *userInfo = [NSDictionary dictionaryWithObject:errMsg forKey:NSLocalizedDescriptionKey];
    
    return [NSError errorWithDomain:GCDAsyncUdpSocketErrorDomain code:GCDAsyncUdpSocketClosedError userInfo:userInfo];
}

- (NSError *)otherError:(NSString *)errMsg
{
    NSDictionary *userInfo = [NSDictionary dictionaryWithObject:errMsg forKey:NSLocalizedDescriptionKey];
    
    return [NSError errorWithDomain:GCDAsyncUdpSocketErrorDomain
                               code:GCDAsyncUdpSocketOtherError
                           userInfo:userInfo];
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Utilities
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

- (BOOL)preOp:(NSError **)errPtr
{
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    
    if (delegate == nil) // Must have delegate set
    {
        if (errPtr)
        {
            NSString *msg = @"Attempting to use socket without a delegate. Set a delegate first.";
            *errPtr = [self badConfigError:msg];
        }
        return NO;
    }
    
    if (delegateQueue == NULL) // Must have delegate queue set
    {
        if (errPtr)
        {
            NSString *msg = @"Attempting to use socket without a delegate queue. Set a delegate queue first.";
            *errPtr = [self badConfigError:msg];
        }
        return NO;
    }
    
    return YES;
}

/**
 * This method executes on a global concurrent queue.
 * When complete, it executes the given completion block on the socketQueue.
 **/
- (void)asyncResolveHost:(NSString *)aHost
                    port:(uint16_t)port
     withCompletionBlock:(void (^)(NSArray *addresses, NSError *error))completionBlock
{
    LogTrace();
    
    // Check parameter(s)
    
    if (aHost == nil)
    {
        NSString *msg = @"The host param is nil. Should be domain name or IP address string.";
        NSError *error = [self badParamError:msg];
        
        // We should still use dispatch_async since this method is expected to be asynchronous
        
        dispatch_async(socketQueue, ^{ @autoreleasepool {
            
            completionBlock(nil, error);
        }});
        
        return;
    }
    
    // It's possible that the given aHost parameter is actually a NSMutableString.
    // So we want to copy it now, within this block that will be executed synchronously.
    // This way the asynchronous lookup block below doesn't have to worry about it changing.
    
    NSString *host = [aHost copy];
    
    
    dispatch_queue_t globalConcurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(globalConcurrentQueue, ^{ @autoreleasepool {
        
        NSMutableArray *addresses = [NSMutableArray arrayWithCapacity:2];
        NSError *error = nil;
        
        if ([host isEqualToString:@"localhost"] || [host isEqualToString:@"loopback"])
        {
            // Use LOOPBACK address
            struct sockaddr_in sockaddr4;
            memset(&sockaddr4, 0, sizeof(sockaddr4));
            
            sockaddr4.sin_len         = sizeof(struct sockaddr_in);
            sockaddr4.sin_family      = AF_INET;
            sockaddr4.sin_port        = htons(port);
            sockaddr4.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
            
            struct sockaddr_in6 sockaddr6;
            memset(&sockaddr6, 0, sizeof(sockaddr6));
            
            sockaddr6.sin6_len       = sizeof(struct sockaddr_in6);
            sockaddr6.sin6_family    = AF_INET6;
            sockaddr6.sin6_port      = htons(port);
            sockaddr6.sin6_addr      = in6addr_loopback;
            
            // Wrap the native address structures and add to list
            [addresses addObject:[NSData dataWithBytes:&sockaddr4 length:sizeof(sockaddr4)]];
            [addresses addObject:[NSData dataWithBytes:&sockaddr6 length:sizeof(sockaddr6)]];
        }
        else
        {
            NSString *portStr = [NSString stringWithFormat:@"%hu", port];
            
            struct addrinfo hints, *res, *res0;
            
            memset(&hints, 0, sizeof(hints));
            hints.ai_family   = PF_UNSPEC;
            hints.ai_socktype = SOCK_DGRAM;
            hints.ai_protocol = IPPROTO_UDP;
            
            int gai_error = getaddrinfo([host UTF8String], [portStr UTF8String], &hints, &res0);
            
            if (gai_error)
            {
                error = [self gaiError:gai_error];
            }
            else
            {
                for(res = res0; res; res = res->ai_next)
                {
                    if (res->ai_family == AF_INET)
                    {
                        // Found IPv4 address
                        // Wrap the native address structure and add to list
                        
                        [addresses addObject:[NSData dataWithBytes:res->ai_addr length:res->ai_addrlen]];
                    }
                    else if (res->ai_family == AF_INET6)
                    {
                        // Found IPv6 address
                        // Wrap the native address structure and add to list
                        
                        [addresses addObject:[NSData dataWithBytes:res->ai_addr length:res->ai_addrlen]];
                    }
                }
                freeaddrinfo(res0);
                
                if ([addresses count] == 0)
                {
                    error = [self gaiError:EAI_FAIL];
                }
            }
        }
        
        dispatch_async(socketQueue, ^{ @autoreleasepool {
            
            completionBlock(addresses, error);
        }});
        
    }});
}

/**
 * This method picks an address from the given list of addresses.
 * The address picked depends upon which protocols are disabled, deactived, & preferred.
 *
 * Returns the address family (AF_INET or AF_INET6) of the picked address,
 * or AF_UNSPEC and the corresponding error is there's a problem.
 **/
- (int)getAddress:(NSData **)addressPtr error:(NSError **)errorPtr fromAddresses:(NSArray *)addresses
{
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    NSAssert([addresses count] > 0, @"Expected at least one address");
    
    int resultAF = AF_UNSPEC;
    NSData *resultAddress = nil;
    NSError *resultError = nil;
    
    // Check for problems
    
    BOOL resolvedIPv4Address = NO;
    BOOL resolvedIPv6Address = NO;
    
    for (NSData *address in addresses)
    {
        switch ([[self class] familyFromAddress:address])
        {
            case AF_INET  : resolvedIPv4Address = YES; break;
            case AF_INET6 : resolvedIPv6Address = YES; break;
                
            default       : NSAssert(NO, @"Addresses array contains invalid address");
        }
    }
    
    BOOL isIPv4Disabled = (config & kIPv4Disabled) ? YES : NO;
    BOOL isIPv6Disabled = (config & kIPv6Disabled) ? YES : NO;
    
    if (isIPv4Disabled && !resolvedIPv6Address)
    {
        NSString *msg = @"IPv4 has been disabled and DNS lookup found no IPv6 address(es).";
        resultError = [self otherError:msg];
        
        if (addressPtr) *addressPtr = resultAddress;
        if (errorPtr) *errorPtr = resultError;
        
        return resultAF;
    }
    
    if (isIPv6Disabled && !resolvedIPv4Address)
    {
        NSString *msg = @"IPv6 has been disabled and DNS lookup found no IPv4 address(es).";
        resultError = [self otherError:msg];
        
        if (addressPtr) *addressPtr = resultAddress;
        if (errorPtr) *errorPtr = resultError;
        
        return resultAF;
    }
    
    BOOL isIPv4Deactivated = (flags & kIPv4Deactivated) ? YES : NO;
    BOOL isIPv6Deactivated = (flags & kIPv6Deactivated) ? YES : NO;
    
    if (isIPv4Deactivated && !resolvedIPv6Address)
    {
        NSString *msg = @"IPv4 has been deactivated due to bind/connect, and DNS lookup found no IPv6 address(es).";
        resultError = [self otherError:msg];
        
        if (addressPtr) *addressPtr = resultAddress;
        if (errorPtr) *errorPtr = resultError;
        
        return resultAF;
    }
    
    if (isIPv6Deactivated && !resolvedIPv4Address)
    {
        NSString *msg = @"IPv6 has been deactivated due to bind/connect, and DNS lookup found no IPv4 address(es).";
        resultError = [self otherError:msg];
        
        if (addressPtr) *addressPtr = resultAddress;
        if (errorPtr) *errorPtr = resultError;
        
        return resultAF;
    }
    
    // Extract first IPv4 and IPv6 address in list
    
    BOOL ipv4WasFirstInList = YES;
    NSData *address4 = nil;
    NSData *address6 = nil;
    
    for (NSData *address in addresses)
    {
        int af = [[self class] familyFromAddress:address];
        
        if (af == AF_INET)
        {
            if (address4 == nil)
            {
                address4 = address;
                
                if (address6)
                    break;
                else
                    ipv4WasFirstInList = YES;
            }
        }
        else // af == AF_INET6
        {
            if (address6 == nil)
            {
                address6 = address;
                
                if (address4)
                    break;
                else
                    ipv4WasFirstInList = NO;
            }
        }
    }
    
    // Determine socket type
    
    BOOL preferIPv4 = (config & kPreferIPv4) ? YES : NO;
    BOOL preferIPv6 = (config & kPreferIPv6) ? YES : NO;
    
    BOOL useIPv4 = ((preferIPv4 && address4) || (address6 == nil));
    BOOL useIPv6 = ((preferIPv6 && address6) || (address4 == nil));
    
    NSAssert(!(preferIPv4 && preferIPv6), @"Invalid config state");
    NSAssert(!(useIPv4 && useIPv6), @"Invalid logic");
    
    if (useIPv4 || (!useIPv6 && ipv4WasFirstInList))
    {
        resultAF = AF_INET;
        resultAddress = address4;
    }
    else
    {
        resultAF = AF_INET6;
        resultAddress = address6;
    }
    
    if (addressPtr) *addressPtr = resultAddress;
    if (errorPtr) *errorPtr = resultError;
    
    return resultAF;
}

/**
 * Finds the address(es) of an interface description.
 * An inteface description may be an interface name (en0, en1, lo0) or corresponding IP (192.168.4.34).
 **/
- (void)convertIntefaceDescription:(NSString *)interfaceDescription
                              port:(uint16_t)port
                      intoAddress4:(NSData **)interfaceAddr4Ptr
                          address6:(NSData **)interfaceAddr6Ptr
{
    NSData *addr4 = nil;
    NSData *addr6 = nil;
    
    if (interfaceDescription == nil)
    {
        // ANY address
        
        struct sockaddr_in sockaddr4;
        memset(&sockaddr4, 0, sizeof(sockaddr4));
        
        sockaddr4.sin_len         = sizeof(sockaddr4);
        sockaddr4.sin_family      = AF_INET;
        sockaddr4.sin_port        = htons(port);
        sockaddr4.sin_addr.s_addr = htonl(INADDR_ANY);
        
        struct sockaddr_in6 sockaddr6;
        memset(&sockaddr6, 0, sizeof(sockaddr6));
        
        sockaddr6.sin6_len       = sizeof(sockaddr6);
        sockaddr6.sin6_family    = AF_INET6;
        sockaddr6.sin6_port      = htons(port);
        sockaddr6.sin6_addr      = in6addr_any;
        
        addr4 = [NSData dataWithBytes:&sockaddr4 length:sizeof(sockaddr4)];
        addr6 = [NSData dataWithBytes:&sockaddr6 length:sizeof(sockaddr6)];
    }
    else if ([interfaceDescription isEqualToString:@"localhost"] ||
             [interfaceDescription isEqualToString:@"loopback"])
    {
        // LOOPBACK address
        
        struct sockaddr_in sockaddr4;
        memset(&sockaddr4, 0, sizeof(sockaddr4));
        
        sockaddr4.sin_len         = sizeof(struct sockaddr_in);
        sockaddr4.sin_family      = AF_INET;
        sockaddr4.sin_port        = htons(port);
        sockaddr4.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
        
        struct sockaddr_in6 sockaddr6;
        memset(&sockaddr6, 0, sizeof(sockaddr6));
        
        sockaddr6.sin6_len       = sizeof(struct sockaddr_in6);
        sockaddr6.sin6_family    = AF_INET6;
        sockaddr6.sin6_port      = htons(port);
        sockaddr6.sin6_addr      = in6addr_loopback;
        
        addr4 = [NSData dataWithBytes:&sockaddr4 length:sizeof(sockaddr4)];
        addr6 = [NSData dataWithBytes:&sockaddr6 length:sizeof(sockaddr6)];
    }
    else
    {
        const char *iface = [interfaceDescription UTF8String];
        
        struct ifaddrs *addrs;
        const struct ifaddrs *cursor;
        
        if ((getifaddrs(&addrs) == 0))
        {
            cursor = addrs;
            while (cursor != NULL)
            {
                if ((addr4 == nil) && (cursor->ifa_addr->sa_family == AF_INET))
                {
                    // IPv4
                    
                    struct sockaddr_in *addr = (struct sockaddr_in *)cursor->ifa_addr;
                    
                    if (strcmp(cursor->ifa_name, iface) == 0)
                    {
                        // Name match
                        
                        struct sockaddr_in nativeAddr4 = *addr;
                        nativeAddr4.sin_port = htons(port);
                        
                        addr4 = [NSData dataWithBytes:&nativeAddr4 length:sizeof(nativeAddr4)];
                    }
                    else
                    {
                        char ip[INET_ADDRSTRLEN];
                        
                        const char *conversion;
                        conversion = inet_ntop(AF_INET, &addr->sin_addr, ip, sizeof(ip));
                        
                        if ((conversion != NULL) && (strcmp(ip, iface) == 0))
                        {
                            // IP match
                            
                            struct sockaddr_in nativeAddr4 = *addr;
                            nativeAddr4.sin_port = htons(port);
                            
                            addr4 = [NSData dataWithBytes:&nativeAddr4 length:sizeof(nativeAddr4)];
                        }
                    }
                }
                else if ((addr6 == nil) && (cursor->ifa_addr->sa_family == AF_INET6))
                {
                    // IPv6
                    
                    struct sockaddr_in6 *addr = (struct sockaddr_in6 *)cursor->ifa_addr;
                    
                    if (strcmp(cursor->ifa_name, iface) == 0)
                    {
                        // Name match
                        
                        struct sockaddr_in6 nativeAddr6 = *addr;
                        nativeAddr6.sin6_port = htons(port);
                        
                        addr6 = [NSData dataWithBytes:&nativeAddr6 length:sizeof(nativeAddr6)];
                    }
                    else
                    {
                        char ip[INET6_ADDRSTRLEN];
                        
                        const char *conversion;
                        conversion = inet_ntop(AF_INET6, &addr->sin6_addr, ip, sizeof(ip));
                        
                        if ((conversion != NULL) && (strcmp(ip, iface) == 0))
                        {
                            // IP match
                            
                            struct sockaddr_in6 nativeAddr6 = *addr;
                            nativeAddr6.sin6_port = htons(port);
                            
                            addr6 = [NSData dataWithBytes:&nativeAddr6 length:sizeof(nativeAddr6)];
                        }
                    }
                }
                
                cursor = cursor->ifa_next;
            }
            
            freeifaddrs(addrs);
        }
    }
    
    if (interfaceAddr4Ptr) *interfaceAddr4Ptr = addr4;
    if (interfaceAddr6Ptr) *interfaceAddr6Ptr = addr6;
}

/**
 * Converts a numeric hostname into its corresponding address.
 * The hostname is expected to be an IPv4 or IPv6 address represented as a human-readable string. (e.g. 192.168.4.34)
 **/
- (void)convertNumericHost:(NSString *)numericHost
                      port:(uint16_t)port
              intoAddress4:(NSData **)addr4Ptr
                  address6:(NSData **)addr6Ptr
{
    NSData *addr4 = nil;
    NSData *addr6 = nil;
    
    if (numericHost)
    {
        NSString *portStr = [NSString stringWithFormat:@"%hu", port];
        
        struct addrinfo hints, *res, *res0;
        
        memset(&hints, 0, sizeof(hints));
        hints.ai_family   = PF_UNSPEC;
        hints.ai_socktype = SOCK_DGRAM;
        hints.ai_protocol = IPPROTO_UDP;
        hints.ai_flags    = AI_NUMERICHOST; // No name resolution should be attempted
        
        if (getaddrinfo([numericHost UTF8String], [portStr UTF8String], &hints, &res0) == 0)
        {
            for (res = res0; res; res = res->ai_next)
            {
                if ((addr4 == nil) && (res->ai_family == AF_INET))
                {
                    // Found IPv4 address
                    // Wrap the native address structure
                    addr4 = [NSData dataWithBytes:res->ai_addr length:res->ai_addrlen];
                }
                else if ((addr6 == nil) && (res->ai_family == AF_INET6))
                {
                    // Found IPv6 address
                    // Wrap the native address structure
                    addr6 = [NSData dataWithBytes:res->ai_addr length:res->ai_addrlen];
                }
            }
            freeaddrinfo(res0);
        }
    }
    
    if (addr4Ptr) *addr4Ptr = addr4;
    if (addr6Ptr) *addr6Ptr = addr6;
}

- (BOOL)isConnectedToAddress4:(NSData *)someAddr4
{
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    NSAssert(flags & kDidConnect, @"Not connected");
    NSAssert(cachedConnectedAddress, @"Expected cached connected address");
    
    if (cachedConnectedFamily != AF_INET)
    {
        return NO;
    }
    
    const struct sockaddr_in *sSockaddr4 = (struct sockaddr_in *)[someAddr4 bytes];
    const struct sockaddr_in *cSockaddr4 = (struct sockaddr_in *)[cachedConnectedAddress bytes];
    
    if (memcmp(&sSockaddr4->sin_addr, &cSockaddr4->sin_addr, sizeof(struct in_addr)) != 0)
    {
        return NO;
    }
    if (memcmp(&sSockaddr4->sin_port, &cSockaddr4->sin_port, sizeof(in_port_t)) != 0)
    {
        return NO;
    }
    
    return YES;
}

- (BOOL)isConnectedToAddress6:(NSData *)someAddr6
{
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    NSAssert(flags & kDidConnect, @"Not connected");
    NSAssert(cachedConnectedAddress, @"Expected cached connected address");
    
    if (cachedConnectedFamily != AF_INET6)
    {
        return NO;
    }
    
    const struct sockaddr_in6 *sSockaddr6 = (struct sockaddr_in6 *)[someAddr6 bytes];
    const struct sockaddr_in6 *cSockaddr6 = (struct sockaddr_in6 *)[cachedConnectedAddress bytes];
    
    if (memcmp(&sSockaddr6->sin6_addr, &cSockaddr6->sin6_addr, sizeof(struct in6_addr)) != 0)
    {
        return NO;
    }
    if (memcmp(&sSockaddr6->sin6_port, &cSockaddr6->sin6_port, sizeof(in_port_t)) != 0)
    {
        return NO;
    }
    
    return YES;
}

- (unsigned int)indexOfInterfaceAddr4:(NSData *)interfaceAddr4
{
    if (interfaceAddr4 == nil)
        return 0;
    if ([interfaceAddr4 length] != sizeof(struct sockaddr_in))
        return 0;
    
    int result = 0;
    struct sockaddr_in *ifaceAddr = (struct sockaddr_in *)[interfaceAddr4 bytes];
    
    struct ifaddrs *addrs;
    const struct ifaddrs *cursor;
    
    if ((getifaddrs(&addrs) == 0))
    {
        cursor = addrs;
        while (cursor != NULL)
        {
            if (cursor->ifa_addr->sa_family == AF_INET)
            {
                // IPv4
                
                struct sockaddr_in *addr = (struct sockaddr_in *)cursor->ifa_addr;
                
                if (memcmp(&addr->sin_addr, &ifaceAddr->sin_addr, sizeof(struct in_addr)) == 0)
                {
                    result = if_nametoindex(cursor->ifa_name);
                    break;
                }
            }
            
            cursor = cursor->ifa_next;
        }
        
        freeifaddrs(addrs);
    }
    
    return result;
}

- (unsigned int)indexOfInterfaceAddr6:(NSData *)interfaceAddr6
{
    if (interfaceAddr6 == nil)
        return 0;
    if ([interfaceAddr6 length] != sizeof(struct sockaddr_in6))
        return 0;
    
    int result = 0;
    struct sockaddr_in6 *ifaceAddr = (struct sockaddr_in6 *)[interfaceAddr6 bytes];
    
    struct ifaddrs *addrs;
    const struct ifaddrs *cursor;
    
    if ((getifaddrs(&addrs) == 0))
    {
        cursor = addrs;
        while (cursor != NULL)
        {
            if (cursor->ifa_addr->sa_family == AF_INET6)
            {
                // IPv6
                
                struct sockaddr_in6 *addr = (struct sockaddr_in6 *)cursor->ifa_addr;
                
                if (memcmp(&addr->sin6_addr, &ifaceAddr->sin6_addr, sizeof(struct in6_addr)) == 0)
                {
                    result = if_nametoindex(cursor->ifa_name);
                    break;
                }
            }
            
            cursor = cursor->ifa_next;
        }
        
        freeifaddrs(addrs);
    }
    
    return result;
}

- (void)setupSendAndReceiveSourcesForSocket4
{
    LogTrace();
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    
    send4Source = dispatch_source_create(DISPATCH_SOURCE_TYPE_WRITE, socket4FD, 0, socketQueue);
    receive4Source = dispatch_source_create(DISPATCH_SOURCE_TYPE_READ, socket4FD, 0, socketQueue);
    
    // Setup event handlers
    
    dispatch_source_set_event_handler(send4Source, ^{ @autoreleasepool {
        
        LogVerbose(@"send4EventBlock");
        LogVerbose(@"dispatch_source_get_data(send4Source) = %lu", dispatch_source_get_data(send4Source));
        
        flags |= kSock4CanAcceptBytes;
        
        // If we're ready to send data, do so immediately.
        // Otherwise pause the send source or it will continue to fire over and over again.
        
        if (currentSend == nil)
        {
            LogVerbose(@"Nothing to send");
            [self suspendSend4Source];
        }
        else if (currentSend->resolveInProgress)
        {
            LogVerbose(@"currentSend - waiting for address resolve");
            [self suspendSend4Source];
        }
        else if (currentSend->filterInProgress)
        {
            LogVerbose(@"currentSend - waiting on sendFilter");
            [self suspendSend4Source];
        }
        else
        {
            [self doSend];
        }
        
    }});
    
    dispatch_source_set_event_handler(receive4Source, ^{ @autoreleasepool {
        
        LogVerbose(@"receive4EventBlock");
        
        socket4FDBytesAvailable = dispatch_source_get_data(receive4Source);
        LogVerbose(@"socket4FDBytesAvailable: %lu", socket4FDBytesAvailable);
        
        if (socket4FDBytesAvailable > 0)
            [self doReceive];
        else
            [self doReceiveEOF];
        
    }});
    
    // Setup cancel handlers
    
    __block int socketFDRefCount = 2;
    
    int theSocketFD = socket4FD;
    
#if !OS_OBJECT_USE_OBJC
    dispatch_source_t theSendSource = send4Source;
    dispatch_source_t theReceiveSource = receive4Source;
#endif
    
    dispatch_source_set_cancel_handler(send4Source, ^{
        
        LogVerbose(@"send4CancelBlock");
        
#if !OS_OBJECT_USE_OBJC
        LogVerbose(@"dispatch_release(send4Source)");
        dispatch_release(theSendSource);
#endif
        
        if (--socketFDRefCount == 0)
        {
            LogVerbose(@"close(socket4FD)");
            close(theSocketFD);
        }
    });
    
    dispatch_source_set_cancel_handler(receive4Source, ^{
        
        LogVerbose(@"receive4CancelBlock");
        
#if !OS_OBJECT_USE_OBJC
        LogVerbose(@"dispatch_release(receive4Source)");
        dispatch_release(theReceiveSource);
#endif
        
        if (--socketFDRefCount == 0)
        {
            LogVerbose(@"close(socket4FD)");
            close(theSocketFD);
        }
    });
    
    // We will not be able to receive until the socket is bound to a port,
    // either explicitly via bind, or implicitly by connect or by sending data.
    //
    // But we should be able to send immediately.
    
    socket4FDBytesAvailable = 0;
    flags |= kSock4CanAcceptBytes;
    
    flags |= kSend4SourceSuspended;
    flags |= kReceive4SourceSuspended;
}

- (void)setupSendAndReceiveSourcesForSocket6
{
    LogTrace();
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    
    send6Source = dispatch_source_create(DISPATCH_SOURCE_TYPE_WRITE, socket6FD, 0, socketQueue);
    receive6Source = dispatch_source_create(DISPATCH_SOURCE_TYPE_READ, socket6FD, 0, socketQueue);
    
    // Setup event handlers
    
    dispatch_source_set_event_handler(send6Source, ^{ @autoreleasepool {
        
        LogVerbose(@"send6EventBlock");
        LogVerbose(@"dispatch_source_get_data(send6Source) = %lu", dispatch_source_get_data(send6Source));
        
        flags |= kSock6CanAcceptBytes;
        
        // If we're ready to send data, do so immediately.
        // Otherwise pause the send source or it will continue to fire over and over again.
        
        if (currentSend == nil)
        {
            LogVerbose(@"Nothing to send");
            [self suspendSend6Source];
        }
        else if (currentSend->resolveInProgress)
        {
            LogVerbose(@"currentSend - waiting for address resolve");
            [self suspendSend6Source];
        }
        else if (currentSend->filterInProgress)
        {
            LogVerbose(@"currentSend - waiting on sendFilter");
            [self suspendSend6Source];
        }
        else
        {
            [self doSend];
        }
        
    }});
    
    dispatch_source_set_event_handler(receive6Source, ^{ @autoreleasepool {
        
        LogVerbose(@"receive6EventBlock");
        
        socket6FDBytesAvailable = dispatch_source_get_data(receive6Source);
        LogVerbose(@"socket6FDBytesAvailable: %lu", socket6FDBytesAvailable);
        
        if (socket6FDBytesAvailable > 0)
            [self doReceive];
        else
            [self doReceiveEOF];
        
    }});
    
    // Setup cancel handlers
    
    __block int socketFDRefCount = 2;
    
    int theSocketFD = socket6FD;
    
#if !OS_OBJECT_USE_OBJC
    dispatch_source_t theSendSource = send6Source;
    dispatch_source_t theReceiveSource = receive6Source;
#endif
    
    dispatch_source_set_cancel_handler(send6Source, ^{
        
        LogVerbose(@"send6CancelBlock");
        
#if !OS_OBJECT_USE_OBJC
        LogVerbose(@"dispatch_release(send6Source)");
        dispatch_release(theSendSource);
#endif
        
        if (--socketFDRefCount == 0)
        {
            LogVerbose(@"close(socket6FD)");
            close(theSocketFD);
        }
    });
    
    dispatch_source_set_cancel_handler(receive6Source, ^{
        
        LogVerbose(@"receive6CancelBlock");
        
#if !OS_OBJECT_USE_OBJC
        LogVerbose(@"dispatch_release(receive6Source)");
        dispatch_release(theReceiveSource);
#endif
        
        if (--socketFDRefCount == 0)
        {
            LogVerbose(@"close(socket6FD)");
            close(theSocketFD);
        }
    });
    
    // We will not be able to receive until the socket is bound to a port,
    // either explicitly via bind, or implicitly by connect or by sending data.
    //
    // But we should be able to send immediately.
    
    socket6FDBytesAvailable = 0;
    flags |= kSock6CanAcceptBytes;
    
    flags |= kSend6SourceSuspended;
    flags |= kReceive6SourceSuspended;
}

- (BOOL)createSocket4:(BOOL)useIPv4 socket6:(BOOL)useIPv6 error:(NSError **)errPtr
{
    LogTrace();
    
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    NSAssert(((flags & kDidCreateSockets) == 0), @"Sockets have already been created");
    
    // CreateSocket Block
    // This block will be invoked below.
    
    int(^createSocket)(int) = ^int (int domain) {
        
        int socketFD = socket(domain, SOCK_DGRAM, 0);
        
        if (socketFD == SOCKET_NULL)
        {
            if (errPtr)
                *errPtr = [self errnoErrorWithReason:@"Error in socket() function"];
            
            return SOCKET_NULL;
        }
        
        int status;
        
        // Set socket options
        
        status = fcntl(socketFD, F_SETFL, O_NONBLOCK);
        if (status == -1)
        {
            if (errPtr)
                *errPtr = [self errnoErrorWithReason:@"Error enabling non-blocking IO on socket (fcntl)"];
            
            close(socketFD);
            return SOCKET_NULL;
        }
        
        int reuseaddr = 1;
        status = setsockopt(socketFD, SOL_SOCKET, SO_REUSEADDR, &reuseaddr, sizeof(reuseaddr));
        if (status == -1)
        {
            if (errPtr)
                *errPtr = [self errnoErrorWithReason:@"Error enabling address reuse (setsockopt)"];
            
            close(socketFD);
            return SOCKET_NULL;
        }
        
        int nosigpipe = 1;
        status = setsockopt(socketFD, SOL_SOCKET, SO_NOSIGPIPE, &nosigpipe, sizeof(nosigpipe));
        if (status == -1)
        {
            if (errPtr)
                *errPtr = [self errnoErrorWithReason:@"Error disabling sigpipe (setsockopt)"];
            
            close(socketFD);
            return SOCKET_NULL;
        }
        
        return socketFD;
    };
    
    // Create sockets depending upon given configuration.
    
    if (useIPv4)
    {
        LogVerbose(@"Creating IPv4 socket");
        
        socket4FD = createSocket(AF_INET);
        if (socket4FD == SOCKET_NULL)
        {
            // errPtr set in local createSocket() block
            return NO;
        }
    }
    
    if (useIPv6)
    {
        LogVerbose(@"Creating IPv6 socket");
        
        socket6FD = createSocket(AF_INET6);
        if (socket6FD == SOCKET_NULL)
        {
            // errPtr set in local createSocket() block
            
            if (socket4FD != SOCKET_NULL)
            {
                close(socket4FD);
                socket4FD = SOCKET_NULL;
            }
            
            return NO;
        }
    }
    
    // Setup send and receive sources
    
    if (useIPv4)
        [self setupSendAndReceiveSourcesForSocket4];
    if (useIPv6)
        [self setupSendAndReceiveSourcesForSocket6];
    
    flags |= kDidCreateSockets;
    return YES;
}

- (BOOL)createSockets:(NSError **)errPtr
{
    LogTrace();
    
    BOOL useIPv4 = [self isIPv4Enabled];
    BOOL useIPv6 = [self isIPv6Enabled];
    
    return [self createSocket4:useIPv4 socket6:useIPv6 error:errPtr];
}

- (void)suspendSend4Source
{
    if (send4Source && !(flags & kSend4SourceSuspended))
    {
        LogVerbose(@"dispatch_suspend(send4Source)");
        
        dispatch_suspend(send4Source);
        flags |= kSend4SourceSuspended;
    }
}

- (void)suspendSend6Source
{
    if (send6Source && !(flags & kSend6SourceSuspended))
    {
        LogVerbose(@"dispatch_suspend(send6Source)");
        
        dispatch_suspend(send6Source);
        flags |= kSend6SourceSuspended;
    }
}

- (void)resumeSend4Source
{
    if (send4Source && (flags & kSend4SourceSuspended))
    {
        LogVerbose(@"dispatch_resume(send4Source)");
        
        dispatch_resume(send4Source);
        flags &= ~kSend4SourceSuspended;
    }
}

- (void)resumeSend6Source
{
    if (send6Source && (flags & kSend6SourceSuspended))
    {
        LogVerbose(@"dispatch_resume(send6Source)");
        
        dispatch_resume(send6Source);
        flags &= ~kSend6SourceSuspended;
    }
}

- (void)suspendReceive4Source
{
    if (receive4Source && !(flags & kReceive4SourceSuspended))
    {
        LogVerbose(@"dispatch_suspend(receive4Source)");
        
        dispatch_suspend(receive4Source);
        flags |= kReceive4SourceSuspended;
    }
}

- (void)suspendReceive6Source
{
    if (receive6Source && !(flags & kReceive6SourceSuspended))
    {
        LogVerbose(@"dispatch_suspend(receive6Source)");
        
        dispatch_suspend(receive6Source);
        flags |= kReceive6SourceSuspended;
    }
}

- (void)resumeReceive4Source
{
    if (receive4Source && (flags & kReceive4SourceSuspended))
    {
        LogVerbose(@"dispatch_resume(receive4Source)");
        
        dispatch_resume(receive4Source);
        flags &= ~kReceive4SourceSuspended;
    }
}

- (void)resumeReceive6Source
{
    if (receive6Source && (flags & kReceive6SourceSuspended))
    {
        LogVerbose(@"dispatch_resume(receive6Source)");
        
        dispatch_resume(receive6Source);
        flags &= ~kReceive6SourceSuspended;
    }
}

- (void)closeSocket4
{
    if (socket4FD != SOCKET_NULL)
    {
        LogVerbose(@"dispatch_source_cancel(send4Source)");
        dispatch_source_cancel(send4Source);
        
        LogVerbose(@"dispatch_source_cancel(receive4Source)");
        dispatch_source_cancel(receive4Source);
        
        // For some crazy reason (in my opinion), cancelling a dispatch source doesn't
        // invoke the cancel handler if the dispatch source is paused.
        // So we have to unpause the source if needed.
        // This allows the cancel handler to be run, which in turn releases the source and closes the socket.
        
        [self resumeSend4Source];
        [self resumeReceive4Source];
        
        // The sockets will be closed by the cancel handlers of the corresponding source
        
        send4Source = NULL;
        receive4Source = NULL;
        
        socket4FD = SOCKET_NULL;
        
        // Clear socket states
        
        socket4FDBytesAvailable = 0;
        flags &= ~kSock4CanAcceptBytes;
        
        // Clear cached info
        
        cachedLocalAddress4 = nil;
        cachedLocalHost4 = nil;
        cachedLocalPort4 = 0;
    }
}

- (void)closeSocket6
{
    if (socket6FD != SOCKET_NULL)
    {
        LogVerbose(@"dispatch_source_cancel(send6Source)");
        dispatch_source_cancel(send6Source);
        
        LogVerbose(@"dispatch_source_cancel(receive6Source)");
        dispatch_source_cancel(receive6Source);
        
        // For some crazy reason (in my opinion), cancelling a dispatch source doesn't
        // invoke the cancel handler if the dispatch source is paused.
        // So we have to unpause the source if needed.
        // This allows the cancel handler to be run, which in turn releases the source and closes the socket.
        
        [self resumeSend6Source];
        [self resumeReceive6Source];
        
        send6Source = NULL;
        receive6Source = NULL;
        
        // The sockets will be closed by the cancel handlers of the corresponding source
        
        socket6FD = SOCKET_NULL;
        
        // Clear socket states
        
        socket6FDBytesAvailable = 0;
        flags &= ~kSock6CanAcceptBytes;
        
        // Clear cached info
        
        cachedLocalAddress6 = nil;
        cachedLocalHost6 = nil;
        cachedLocalPort6 = 0;
    }
}

- (void)closeSockets
{
    [self closeSocket4];
    [self closeSocket6];
    
    flags &= ~kDidCreateSockets;
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Diagnostics
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

- (BOOL)getLocalAddress:(NSData **)dataPtr
                   host:(NSString **)hostPtr
                   port:(uint16_t *)portPtr
              forSocket:(int)socketFD
             withFamily:(int)socketFamily
{
    
    NSData   *data = nil;
    NSString *host = nil;
    uint16_t  port = 0;
    
    if (socketFamily == AF_INET)
    {
        struct sockaddr_in sockaddr4;
        socklen_t sockaddr4len = sizeof(sockaddr4);
        
        if (getsockname(socketFD, (struct sockaddr *)&sockaddr4, &sockaddr4len) == 0)
        {
            data = [NSData dataWithBytes:&sockaddr4 length:sockaddr4len];
            host = [[self class] hostFromSockaddr4:&sockaddr4];
            port = [[self class] portFromSockaddr4:&sockaddr4];
        }
        else
        {
            LogWarn(@"Error in getsockname: %@", [self errnoError]);
        }
    }
    else if (socketFamily == AF_INET6)
    {
        struct sockaddr_in6 sockaddr6;
        socklen_t sockaddr6len = sizeof(sockaddr6);
        
        if (getsockname(socketFD, (struct sockaddr *)&sockaddr6, &sockaddr6len) == 0)
        {
            data = [NSData dataWithBytes:&sockaddr6 length:sockaddr6len];
            host = [[self class] hostFromSockaddr6:&sockaddr6];
            port = [[self class] portFromSockaddr6:&sockaddr6];
        }
        else
        {
            LogWarn(@"Error in getsockname: %@", [self errnoError]);
        }
    }
    
    if (dataPtr) *dataPtr = data;
    if (hostPtr) *hostPtr = host;
    if (portPtr) *portPtr = port;
    
    return (data != nil);
}

- (void)maybeUpdateCachedLocalAddress4Info
{
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    
    if ( cachedLocalAddress4 || ((flags & kDidBind) == 0) || (socket4FD == SOCKET_NULL) )
    {
        return;
    }
    
    NSData *address = nil;
    NSString *host = nil;
    uint16_t port = 0;
    
    if ([self getLocalAddress:&address host:&host port:&port forSocket:socket4FD withFamily:AF_INET])
    {
        
        cachedLocalAddress4 = address;
        cachedLocalHost4 = host;
        cachedLocalPort4 = port;
    }
}

- (void)maybeUpdateCachedLocalAddress6Info
{
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    
    if ( cachedLocalAddress6 || ((flags & kDidBind) == 0) || (socket6FD == SOCKET_NULL) )
    {
        return;
    }
    
    NSData *address = nil;
    NSString *host = nil;
    uint16_t port = 0;
    
    if ([self getLocalAddress:&address host:&host port:&port forSocket:socket6FD withFamily:AF_INET6])
    {
        
        cachedLocalAddress6 = address;
        cachedLocalHost6 = host;
        cachedLocalPort6 = port;
    }
}

- (NSData *)localAddress
{
    __block NSData *result = nil;
    
    dispatch_block_t block = ^{
        
        if (socket4FD != SOCKET_NULL)
        {
            [self maybeUpdateCachedLocalAddress4Info];
            result = cachedLocalAddress4;
        }
        else
        {
            [self maybeUpdateCachedLocalAddress6Info];
            result = cachedLocalAddress6;
        }
        
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, AutoreleasedBlock(block));
    
    return result;
}

- (NSString *)localHost
{
    __block NSString *result = nil;
    
    dispatch_block_t block = ^{
        
        if (socket4FD != SOCKET_NULL)
        {
            [self maybeUpdateCachedLocalAddress4Info];
            result = cachedLocalHost4;
        }
        else
        {
            [self maybeUpdateCachedLocalAddress6Info];
            result = cachedLocalHost6;
        }
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, AutoreleasedBlock(block));
    
    return result;
}

- (uint16_t)localPort
{
    __block uint16_t result = 0;
    
    dispatch_block_t block = ^{
        
        if (socket4FD != SOCKET_NULL)
        {
            [self maybeUpdateCachedLocalAddress4Info];
            result = cachedLocalPort4;
        }
        else
        {
            [self maybeUpdateCachedLocalAddress6Info];
            result = cachedLocalPort6;
        }
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, AutoreleasedBlock(block));
    
    return result;
}

- (NSData *)localAddress_IPv4
{
    __block NSData *result = nil;
    
    dispatch_block_t block = ^{
        
        [self maybeUpdateCachedLocalAddress4Info];
        result = cachedLocalAddress4;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, AutoreleasedBlock(block));
    
    return result;
}

- (NSString *)localHost_IPv4
{
    __block NSString *result = nil;
    
    dispatch_block_t block = ^{
        
        [self maybeUpdateCachedLocalAddress4Info];
        result = cachedLocalHost4;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, AutoreleasedBlock(block));
    
    return result;
}

- (uint16_t)localPort_IPv4
{
    __block uint16_t result = 0;
    
    dispatch_block_t block = ^{
        
        [self maybeUpdateCachedLocalAddress4Info];
        result = cachedLocalPort4;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, AutoreleasedBlock(block));
    
    return result;
}

- (NSData *)localAddress_IPv6
{
    __block NSData *result = nil;
    
    dispatch_block_t block = ^{
        
        [self maybeUpdateCachedLocalAddress6Info];
        result = cachedLocalAddress6;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, AutoreleasedBlock(block));
    
    return result;
}

- (NSString *)localHost_IPv6
{
    __block NSString *result = nil;
    
    dispatch_block_t block = ^{
        
        [self maybeUpdateCachedLocalAddress6Info];
        result = cachedLocalHost6;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, AutoreleasedBlock(block));
    
    return result;
}

- (uint16_t)localPort_IPv6
{
    __block uint16_t result = 0;
    
    dispatch_block_t block = ^{
        
        [self maybeUpdateCachedLocalAddress6Info];
        result = cachedLocalPort6;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, AutoreleasedBlock(block));
    
    return result;
}

- (void)maybeUpdateCachedConnectedAddressInfo
{
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    
    if (cachedConnectedAddress || (flags & kDidConnect) == 0)
    {
        return;
    }
    
    NSData *data = nil;
    NSString *host = nil;
    uint16_t port = 0;
    int family = AF_UNSPEC;
    
    if (socket4FD != SOCKET_NULL)
    {
        struct sockaddr_in sockaddr4;
        socklen_t sockaddr4len = sizeof(sockaddr4);
        
        if (getpeername(socket4FD, (struct sockaddr *)&sockaddr4, &sockaddr4len) == 0)
        {
            data = [NSData dataWithBytes:&sockaddr4 length:sockaddr4len];
            host = [[self class] hostFromSockaddr4:&sockaddr4];
            port = [[self class] portFromSockaddr4:&sockaddr4];
            family = AF_INET;
        }
        else
        {
            LogWarn(@"Error in getpeername: %@", [self errnoError]);
        }
    }
    else if (socket6FD != SOCKET_NULL)
    {
        struct sockaddr_in6 sockaddr6;
        socklen_t sockaddr6len = sizeof(sockaddr6);
        
        if (getpeername(socket6FD, (struct sockaddr *)&sockaddr6, &sockaddr6len) == 0)
        {
            data = [NSData dataWithBytes:&sockaddr6 length:sockaddr6len];
            host = [[self class] hostFromSockaddr6:&sockaddr6];
            port = [[self class] portFromSockaddr6:&sockaddr6];
            family = AF_INET6;
        }
        else
        {
            LogWarn(@"Error in getpeername: %@", [self errnoError]);
        }
    }
    
    
    cachedConnectedAddress = data;
    cachedConnectedHost    = host;
    cachedConnectedPort    = port;
    cachedConnectedFamily  = family;
}

- (NSData *)connectedAddress
{
    __block NSData *result = nil;
    
    dispatch_block_t block = ^{
        
        [self maybeUpdateCachedConnectedAddressInfo];
        result = cachedConnectedAddress;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, AutoreleasedBlock(block));
    
    return result;
}

- (NSString *)connectedHost
{
    __block NSString *result = nil;
    
    dispatch_block_t block = ^{
        
        [self maybeUpdateCachedConnectedAddressInfo];
        result = cachedConnectedHost;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, AutoreleasedBlock(block));
    
    return result;
}

- (uint16_t)connectedPort
{
    __block uint16_t result = 0;
    
    dispatch_block_t block = ^{
        
        [self maybeUpdateCachedConnectedAddressInfo];
        result = cachedConnectedPort;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, AutoreleasedBlock(block));
    
    return result;
}

- (BOOL)isConnected
{
    __block BOOL result = NO;
    
    dispatch_block_t block = ^{
        result = (flags & kDidConnect) ? YES : NO;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    return result;
}

- (BOOL)isClosed
{
    __block BOOL result = YES;
    
    dispatch_block_t block = ^{
        
        result = (flags & kDidCreateSockets) ? NO : YES;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    return result;
}

- (BOOL)isIPv4
{
    __block BOOL result = NO;
    
    dispatch_block_t block = ^{
        
        if (flags & kDidCreateSockets)
        {
            result = (socket4FD != SOCKET_NULL);
        }
        else
        {
            result = [self isIPv4Enabled];
        }
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    return result;
}

- (BOOL)isIPv6
{
    __block BOOL result = NO;
    
    dispatch_block_t block = ^{
        
        if (flags & kDidCreateSockets)
        {
            result = (socket6FD != SOCKET_NULL);
        }
        else
        {
            result = [self isIPv6Enabled];
        }
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    return result;
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Binding
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

/**
 * This method runs through the various checks required prior to a bind attempt.
 * It is shared between the various bind methods.
 **/
- (BOOL)preBind:(NSError **)errPtr
{
    if (![self preOp:errPtr])
    {
        return NO;
    }
    
    if (flags & kDidBind)
    {
        if (errPtr)
        {
            NSString *msg = @"Cannot bind a socket more than once.";
            *errPtr = [self badConfigError:msg];
        }
        return NO;
    }
    
    if ((flags & kConnecting) || (flags & kDidConnect))
    {
        if (errPtr)
        {
            NSString *msg = @"Cannot bind after connecting. If needed, bind first, then connect.";
            *errPtr = [self badConfigError:msg];
        }
        return NO;
    }
    
    BOOL isIPv4Disabled = (config & kIPv4Disabled) ? YES : NO;
    BOOL isIPv6Disabled = (config & kIPv6Disabled) ? YES : NO;
    
    if (isIPv4Disabled && isIPv6Disabled) // Must have IPv4 or IPv6 enabled
    {
        if (errPtr)
        {
            NSString *msg = @"Both IPv4 and IPv6 have been disabled. Must enable at least one protocol first.";
            *errPtr = [self badConfigError:msg];
        }
        return NO;
    }
    
    return YES;
}

- (BOOL)bindToPort:(uint16_t)port error:(NSError **)errPtr
{
    return [self bindToPort:port interface:nil error:errPtr];
}

- (BOOL)bindToPort:(uint16_t)port interface:(NSString *)interface error:(NSError **)errPtr
{
    __block BOOL result = NO;
    __block NSError *err = nil;
    
    dispatch_block_t block = ^{ @autoreleasepool {
        
        // Run through sanity checks
        
        if (![self preBind:&err])
        {
            return_from_block;
        }
        
        // Check the given interface
        
        NSData *interface4 = nil;
        NSData *interface6 = nil;
        
        [self convertIntefaceDescription:interface port:port intoAddress4:&interface4 address6:&interface6];
        
        if ((interface4 == nil) && (interface6 == nil))
        {
            NSString *msg = @"Unknown interface. Specify valid interface by name (e.g. \"en1\") or IP address.";
            err = [self badParamError:msg];
            
            return_from_block;
        }
        
        BOOL isIPv4Disabled = (config & kIPv4Disabled) ? YES : NO;
        BOOL isIPv6Disabled = (config & kIPv6Disabled) ? YES : NO;
        
        if (isIPv4Disabled && (interface6 == nil))
        {
            NSString *msg = @"IPv4 has been disabled and specified interface doesn't support IPv6.";
            err = [self badParamError:msg];
            
            return_from_block;
        }
        
        if (isIPv6Disabled && (interface4 == nil))
        {
            NSString *msg = @"IPv6 has been disabled and specified interface doesn't support IPv4.";
            err = [self badParamError:msg];
            
            return_from_block;
        }
        
        // Determine protocol(s)
        
        BOOL useIPv4 = !isIPv4Disabled && (interface4 != nil);
        BOOL useIPv6 = !isIPv6Disabled && (interface6 != nil);
        
        // Create the socket(s) if needed
        
        if ((flags & kDidCreateSockets) == 0)
        {
            if (![self createSocket4:useIPv4 socket6:useIPv6 error:&err])
            {
                return_from_block;
            }
        }
        
        // Bind the socket(s)
        
        LogVerbose(@"Binding socket to port(%hu) interface(%@)", port, interface);
        
        if (useIPv4)
        {
            int status = bind(socket4FD, (struct sockaddr *)[interface4 bytes], (socklen_t)[interface4 length]);
            if (status == -1)
            {
                [self closeSockets];
                
                NSString *reason = @"Error in bind() function";
                err = [self errnoErrorWithReason:reason];
                
                return_from_block;
            }
        }
        
        if (useIPv6)
        {
            int status = bind(socket6FD, (struct sockaddr *)[interface6 bytes], (socklen_t)[interface6 length]);
            if (status == -1)
            {
                [self closeSockets];
                
                NSString *reason = @"Error in bind() function";
                err = [self errnoErrorWithReason:reason];
                
                return_from_block;
            }
        }
        
        // Update flags
        
        flags |= kDidBind;
        
        if (!useIPv4) flags |= kIPv4Deactivated;
        if (!useIPv6) flags |= kIPv6Deactivated;
        
        result = YES;
        
    }};
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    if (err)
        LogError(@"Error binding to port/interface: %@", err);
    
    if (errPtr)
        *errPtr = err;
    
    return result;
}

- (BOOL)bindToAddress:(NSData *)localAddr error:(NSError **)errPtr
{
    __block BOOL result = NO;
    __block NSError *err = nil;
    
    dispatch_block_t block = ^{ @autoreleasepool {
        
        // Run through sanity checks
        
        if (![self preBind:&err])
        {
            return_from_block;
        }
        
        // Check the given address
        
        int addressFamily = [[self class] familyFromAddress:localAddr];
        
        if (addressFamily == AF_UNSPEC)
        {
            NSString *msg = @"A valid IPv4 or IPv6 address was not given";
            err = [self badParamError:msg];
            
            return_from_block;
        }
        
        NSData *localAddr4 = (addressFamily == AF_INET)  ? localAddr : nil;
        NSData *localAddr6 = (addressFamily == AF_INET6) ? localAddr : nil;
        
        BOOL isIPv4Disabled = (config & kIPv4Disabled) ? YES : NO;
        BOOL isIPv6Disabled = (config & kIPv6Disabled) ? YES : NO;
        
        if (isIPv4Disabled && localAddr4)
        {
            NSString *msg = @"IPv4 has been disabled and an IPv4 address was passed.";
            err = [self badParamError:msg];
            
            return_from_block;
        }
        
        if (isIPv6Disabled && localAddr6)
        {
            NSString *msg = @"IPv6 has been disabled and an IPv6 address was passed.";
            err = [self badParamError:msg];
            
            return_from_block;
        }
        
        // Determine protocol(s)
        
        BOOL useIPv4 = !isIPv4Disabled && (localAddr4 != nil);
        BOOL useIPv6 = !isIPv6Disabled && (localAddr6 != nil);
        
        // Create the socket(s) if needed
        
        if ((flags & kDidCreateSockets) == 0)
        {
            if (![self createSocket4:useIPv4 socket6:useIPv6 error:&err])
            {
                return_from_block;
            }
        }
        
        // Bind the socket(s)
        
        if (useIPv4)
        {
            LogVerbose(@"Binding socket to address(%@:%hu)",
                       [[self class] hostFromAddress:localAddr4],
                       [[self class] portFromAddress:localAddr4]);
            
            int status = bind(socket4FD, (struct sockaddr *)[localAddr4 bytes], (socklen_t)[localAddr4 length]);
            if (status == -1)
            {
                [self closeSockets];
                
                NSString *reason = @"Error in bind() function";
                err = [self errnoErrorWithReason:reason];
                
                return_from_block;
            }
        }
        else
        {
            LogVerbose(@"Binding socket to address(%@:%hu)",
                       [[self class] hostFromAddress:localAddr6],
                       [[self class] portFromAddress:localAddr6]);
            
            int status = bind(socket6FD, (struct sockaddr *)[localAddr6 bytes], (socklen_t)[localAddr6 length]);
            if (status == -1)
            {
                [self closeSockets];
                
                NSString *reason = @"Error in bind() function";
                err = [self errnoErrorWithReason:reason];
                
                return_from_block;
            }
        }
        
        // Update flags
        
        flags |= kDidBind;
        
        if (!useIPv4) flags |= kIPv4Deactivated;
        if (!useIPv6) flags |= kIPv6Deactivated;
        
        result = YES;
        
    }};
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    if (err)
        LogError(@"Error binding to address: %@", err);
    
    if (errPtr)
        *errPtr = err;
    
    return result;
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Connecting
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

/**
 * This method runs through the various checks required prior to a connect attempt.
 * It is shared between the various connect methods.
 **/
- (BOOL)preConnect:(NSError **)errPtr
{
    if (![self preOp:errPtr])
    {
        return NO;
    }
    
    if ((flags & kConnecting) || (flags & kDidConnect))
    {
        if (errPtr)
        {
            NSString *msg = @"Cannot connect a socket more than once.";
            *errPtr = [self badConfigError:msg];
        }
        return NO;
    }
    
    BOOL isIPv4Disabled = (config & kIPv4Disabled) ? YES : NO;
    BOOL isIPv6Disabled = (config & kIPv6Disabled) ? YES : NO;
    
    if (isIPv4Disabled && isIPv6Disabled) // Must have IPv4 or IPv6 enabled
    {
        if (errPtr)
        {
            NSString *msg = @"Both IPv4 and IPv6 have been disabled. Must enable at least one protocol first.";
            *errPtr = [self badConfigError:msg];
        }
        return NO;
    }
    
    return YES;
}

- (BOOL)connectToHost:(NSString *)host onPort:(uint16_t)port error:(NSError **)errPtr
{
    __block BOOL result = NO;
    __block NSError *err = nil;
    
    dispatch_block_t block = ^{ @autoreleasepool {
        
        // Run through sanity checks.
        
        if (![self preConnect:&err])
        {
            return_from_block;
        }
        
        // Check parameter(s)
        
        if (host == nil)
        {
            NSString *msg = @"The host param is nil. Should be domain name or IP address string.";
            err = [self badParamError:msg];
            
            return_from_block;
        }
        
        // Create the socket(s) if needed
        
        if ((flags & kDidCreateSockets) == 0)
        {
            if (![self createSockets:&err])
            {
                return_from_block;
            }
        }
        
        // Create special connect packet
        
        GCDAsyncUdpSpecialPacket *packet = [[GCDAsyncUdpSpecialPacket alloc] init];
        packet->resolveInProgress = YES;
        
        // Start asynchronous DNS resolve for host:port on background queue
        
        LogVerbose(@"Dispatching DNS resolve for connect...");
        
        [self asyncResolveHost:host port:port withCompletionBlock:^(NSArray *addresses, NSError *error) {
            
            // The asyncResolveHost:port:: method asynchronously dispatches a task onto the global concurrent queue,
            // and immediately returns. Once the async resolve task completes,
            // this block is executed on our socketQueue.
            
            packet->resolveInProgress = NO;
            
            packet->addresses = addresses;
            packet->error = error;
            
            [self maybeConnect];
        }];
        
        // Updates flags, add connect packet to send queue, and pump send queue
        
        flags |= kConnecting;
        
        [sendQueue addObject:packet];
        [self maybeDequeueSend];
        
        result = YES;
    }};
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    if (err)
        LogError(@"Error connecting to host/port: %@", err);
    
    if (errPtr)
        *errPtr = err;
    
    return result;
}

- (BOOL)connectToAddress:(NSData *)remoteAddr error:(NSError **)errPtr
{
    __block BOOL result = NO;
    __block NSError *err = nil;
    
    dispatch_block_t block = ^{ @autoreleasepool {
        
        // Run through sanity checks.
        
        if (![self preConnect:&err])
        {
            return_from_block;
        }
        
        // Check parameter(s)
        
        if (remoteAddr == nil)
        {
            NSString *msg = @"The address param is nil. Should be a valid address.";
            err = [self badParamError:msg];
            
            return_from_block;
        }
        
        // Create the socket(s) if needed
        
        if ((flags & kDidCreateSockets) == 0)
        {
            if (![self createSockets:&err])
            {
                return_from_block;
            }
        }
        
        // The remoteAddr parameter could be of type NSMutableData.
        // So we copy it to be safe.
        
        NSData *address = [remoteAddr copy];
        NSArray *addresses = [NSArray arrayWithObject:address];
        
        GCDAsyncUdpSpecialPacket *packet = [[GCDAsyncUdpSpecialPacket alloc] init];
        packet->addresses = addresses;
        
        // Updates flags, add connect packet to send queue, and pump send queue
        
        flags |= kConnecting;
        
        [sendQueue addObject:packet];
        [self maybeDequeueSend];
        
        result = YES;
    }};
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    if (err)
        LogError(@"Error connecting to address: %@", err);
    
    if (errPtr)
        *errPtr = err;
    
    return result;
}

- (void)maybeConnect
{
    LogTrace();
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    
    
    BOOL sendQueueReady = [currentSend isKindOfClass:[GCDAsyncUdpSpecialPacket class]];
    
    if (sendQueueReady)
    {
        GCDAsyncUdpSpecialPacket *connectPacket = (GCDAsyncUdpSpecialPacket *)currentSend;
        
        if (connectPacket->resolveInProgress)
        {
            LogVerbose(@"Waiting for DNS resolve...");
        }
        else
        {
            if (connectPacket->error)
            {
                [self notifyDidNotConnect:connectPacket->error];
            }
            else
            {
                NSData *address = nil;
                NSError *error = nil;
                
                int addressFamily = [self getAddress:&address error:&error fromAddresses:connectPacket->addresses];
                
                // Perform connect
                
                BOOL result = NO;
                
                switch (addressFamily)
                {
                    case AF_INET  : result = [self connectWithAddress4:address error:&error]; break;
                    case AF_INET6 : result = [self connectWithAddress6:address error:&error]; break;
                }
                
                if (result)
                {
                    flags |= kDidBind;
                    flags |= kDidConnect;
                    
                    cachedConnectedAddress = address;
                    cachedConnectedHost = [[self class] hostFromAddress:address];
                    cachedConnectedPort = [[self class] portFromAddress:address];
                    cachedConnectedFamily = addressFamily;
                    
                    [self notifyDidConnectToAddress:address];
                }
                else
                {
                    [self notifyDidNotConnect:error];
                }
            }
            
            flags &= ~kConnecting;
            
            [self endCurrentSend];
            [self maybeDequeueSend];
        }
    }
}

- (BOOL)connectWithAddress4:(NSData *)address4 error:(NSError **)errPtr
{
    LogTrace();
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    
    int status = connect(socket4FD, (struct sockaddr *)[address4 bytes], (socklen_t)[address4 length]);
    if (status != 0)
    {
        if (errPtr)
            *errPtr = [self errnoErrorWithReason:@"Error in connect() function"];
        
        return NO;
    }
    
    [self closeSocket6];
    flags |= kIPv6Deactivated;
    
    return YES;
}

- (BOOL)connectWithAddress6:(NSData *)address6 error:(NSError **)errPtr
{
    LogTrace();
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    
    int status = connect(socket6FD, (struct sockaddr *)[address6 bytes], (socklen_t)[address6 length]);
    if (status != 0)
    {
        if (errPtr)
            *errPtr = [self errnoErrorWithReason:@"Error in connect() function"];
        
        return NO;
    }
    
    [self closeSocket4];
    flags |= kIPv4Deactivated;
    
    return YES;
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Multicast
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

- (BOOL)preJoin:(NSError **)errPtr
{
    if (![self preOp:errPtr])
    {
        return NO;
    }
    
    if (!(flags & kDidBind))
    {
        if (errPtr)
        {
            NSString *msg = @"Must bind a socket before joining a multicast group.";
            *errPtr = [self badConfigError:msg];
        }
        return NO;
    }
    
    if ((flags & kConnecting) || (flags & kDidConnect))
    {
        if (errPtr)
        {
            NSString *msg = @"Cannot join a multicast group if connected.";
            *errPtr = [self badConfigError:msg];
        }
        return NO;
    }
    
    return YES;
}

- (BOOL)joinMulticastGroup:(NSString *)group error:(NSError **)errPtr
{
    return [self joinMulticastGroup:group onInterface:nil error:errPtr];
}

- (BOOL)joinMulticastGroup:(NSString *)group onInterface:(NSString *)interface error:(NSError **)errPtr
{
    // IP_ADD_MEMBERSHIP == IPV6_JOIN_GROUP
    return [self performMulticastRequest:IP_ADD_MEMBERSHIP forGroup:group onInterface:interface error:errPtr];
}

- (BOOL)leaveMulticastGroup:(NSString *)group error:(NSError **)errPtr
{
    return [self leaveMulticastGroup:group onInterface:nil error:errPtr];
}

- (BOOL)leaveMulticastGroup:(NSString *)group onInterface:(NSString *)interface error:(NSError **)errPtr
{
    // IP_DROP_MEMBERSHIP == IPV6_LEAVE_GROUP
    return [self performMulticastRequest:IP_DROP_MEMBERSHIP forGroup:group onInterface:interface error:errPtr];
}

- (BOOL)performMulticastRequest:(int)requestType
                       forGroup:(NSString *)group
                    onInterface:(NSString *)interface
                          error:(NSError **)errPtr
{
    __block BOOL result = NO;
    __block NSError *err = nil;
    
    dispatch_block_t block = ^{ @autoreleasepool {
        
        // Run through sanity checks
        
        if (![self preJoin:&err])
        {
            return_from_block;
        }
        
        // Convert group to address
        
        NSData *groupAddr4 = nil;
        NSData *groupAddr6 = nil;
        
        [self convertNumericHost:group port:0 intoAddress4:&groupAddr4 address6:&groupAddr6];
        
        if ((groupAddr4 == nil) && (groupAddr6 == nil))
        {
            NSString *msg = @"Unknown group. Specify valid group IP address.";
            err = [self badParamError:msg];
            
            return_from_block;
        }
        
        // Convert interface to address
        
        NSData *interfaceAddr4 = nil;
        NSData *interfaceAddr6 = nil;
        
        [self convertIntefaceDescription:interface port:0 intoAddress4:&interfaceAddr4 address6:&interfaceAddr6];
        
        if ((interfaceAddr4 == nil) && (interfaceAddr6 == nil))
        {
            NSString *msg = @"Unknown interface. Specify valid interface by name (e.g. \"en1\") or IP address.";
            err = [self badParamError:msg];
            
            return_from_block;
        }
        
        // Perform join
        
        if ((socket4FD != SOCKET_NULL) && groupAddr4 && interfaceAddr4)
        {
            const struct sockaddr_in *nativeGroup = (struct sockaddr_in *)[groupAddr4 bytes];
            const struct sockaddr_in *nativeIface = (struct sockaddr_in *)[interfaceAddr4 bytes];
            
            struct ip_mreq imreq;
            imreq.imr_multiaddr = nativeGroup->sin_addr;
            imreq.imr_interface = nativeIface->sin_addr;
            
            int status = setsockopt(socket4FD, IPPROTO_IP, requestType, (const void *)&imreq, sizeof(imreq));
            if (status != 0)
            {
                err = [self errnoErrorWithReason:@"Error in setsockopt() function"];
                
                return_from_block;
            }
            
            // Using IPv4 only
            [self closeSocket6];
            
            result = YES;
        }
        else if ((socket6FD != SOCKET_NULL) && groupAddr6 && interfaceAddr6)
        {
            const struct sockaddr_in6 *nativeGroup = (struct sockaddr_in6 *)[groupAddr6 bytes];
            
            struct ipv6_mreq imreq;
            imreq.ipv6mr_multiaddr = nativeGroup->sin6_addr;
            imreq.ipv6mr_interface = [self indexOfInterfaceAddr6:interfaceAddr6];
            
            int status = setsockopt(socket6FD, IPPROTO_IPV6, requestType, (const void *)&imreq, sizeof(imreq));
            if (status != 0)
            {
                err = [self errnoErrorWithReason:@"Error in setsockopt() function"];
                
                return_from_block;
            }
            
            // Using IPv6 only
            [self closeSocket4];
            
            result = YES;
        }
        else
        {
            NSString *msg = @"Socket, group, and interface do not have matching IP versions";
            err = [self badParamError:msg];
            
            return_from_block;
        }
        
    }};
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    if (errPtr)
        *errPtr = err;
    
    return result;
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Reuse port
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

- (BOOL)enableReusePort:(BOOL)flag error:(NSError **)errPtr
{
    __block BOOL result = NO;
    __block NSError *err = nil;
    
    dispatch_block_t block = ^{ @autoreleasepool {
        
        if (![self preOp:&err])
        {
            return_from_block;
        }
        
        if ((flags & kDidCreateSockets) == 0)
        {
            if (![self createSockets:&err])
            {
                return_from_block;
            }
        }
        
        int value = flag ? 1 : 0;
        if (socket4FD != SOCKET_NULL)
        {
            int error = setsockopt(socket4FD, SOL_SOCKET, SO_REUSEPORT, (const void *)&value, sizeof(value));
            
            if (error)
            {
                err = [self errnoErrorWithReason:@"Error in setsockopt() function"];
                
                return_from_block;
            }
            result = YES;
        }
        
        if (socket6FD != SOCKET_NULL)
        {
            int error = setsockopt(socket6FD, SOL_SOCKET, SO_REUSEPORT, (const void *)&value, sizeof(value));
            
            if (error)
            {
                err = [self errnoErrorWithReason:@"Error in setsockopt() function"];
                
                return_from_block;
            }
            result = YES;
        }
        
    }};
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    if (errPtr)
        *errPtr = err;
    
    return result;
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Broadcast
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

- (BOOL)enableBroadcast:(BOOL)flag error:(NSError **)errPtr
{
    __block BOOL result = NO;
    __block NSError *err = nil;
    
    dispatch_block_t block = ^{ @autoreleasepool {
        
        if (![self preOp:&err])
        {
            return_from_block;
        }
        
        if ((flags & kDidCreateSockets) == 0)
        {
            if (![self createSockets:&err])
            {
                return_from_block;
            }
        }
        
        if (socket4FD != SOCKET_NULL)
        {
            int value = flag ? 1 : 0;
            int error = setsockopt(socket4FD, SOL_SOCKET, SO_BROADCAST, (const void *)&value, sizeof(value));
            
            if (error)
            {
                err = [self errnoErrorWithReason:@"Error in setsockopt() function"];
                
                return_from_block;
            }
            result = YES;
        }
        
        // IPv6 does not implement broadcast, the ability to send a packet to all hosts on the attached link.
        // The same effect can be achieved by sending a packet to the link-local all hosts multicast group.
        
    }};
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    if (errPtr)
        *errPtr = err;
    
    return result;
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Sending
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

- (void)sendData:(NSData *)data withTag:(long)tag
{
    [self sendData:data withTimeout:-1.0 tag:tag];
}

- (void)sendData:(NSData *)data withTimeout:(NSTimeInterval)timeout tag:(long)tag
{
    LogTrace();
    
    if ([data length] == 0)
    {
        LogWarn(@"Ignoring attempt to send nil/empty data.");
        return;
    }
    
    GCDAsyncUdpSendPacket *packet = [[GCDAsyncUdpSendPacket alloc] initWithData:data timeout:timeout tag:tag];
    
    dispatch_async(socketQueue, ^{ @autoreleasepool {
        
        [sendQueue addObject:packet];
        [self maybeDequeueSend];
    }});
    
}

- (void)sendData:(NSData *)data
          toHost:(NSString *)host
            port:(uint16_t)port
     withTimeout:(NSTimeInterval)timeout
             tag:(long)tag
{
    LogTrace();
    
    if ([data length] == 0)
    {
        LogWarn(@"Ignoring attempt to send nil/empty data.");
        return;
    }
    
    GCDAsyncUdpSendPacket *packet = [[GCDAsyncUdpSendPacket alloc] initWithData:data timeout:timeout tag:tag];
    packet->resolveInProgress = YES;
    
    [self asyncResolveHost:host port:port withCompletionBlock:^(NSArray *addresses, NSError *error) {
        
        // The asyncResolveHost:port:: method asynchronously dispatches a task onto the global concurrent queue,
        // and immediately returns. Once the async resolve task completes,
        // this block is executed on our socketQueue.
        
        packet->resolveInProgress = NO;
        
        packet->resolvedAddresses = addresses;
        packet->resolveError = error;
        
        if (packet == currentSend)
        {
            LogVerbose(@"currentSend - address resolved");
            [self doPreSend];
        }
    }];
    
    dispatch_async(socketQueue, ^{ @autoreleasepool {
        
        [sendQueue addObject:packet];
        [self maybeDequeueSend];
        
    }});
    
}

- (void)sendData:(NSData *)data toAddress:(NSData *)remoteAddr withTimeout:(NSTimeInterval)timeout tag:(long)tag
{
    LogTrace();
    
    if ([data length] == 0)
    {
        LogWarn(@"Ignoring attempt to send nil/empty data.");
        return;
    }
    
    GCDAsyncUdpSendPacket *packet = [[GCDAsyncUdpSendPacket alloc] initWithData:data timeout:timeout tag:tag];
    packet->addressFamily = [GCDAsyncUdpSocket familyFromAddress:remoteAddr];
    packet->address = remoteAddr;
    
    dispatch_async(socketQueue, ^{ @autoreleasepool {
        
        [sendQueue addObject:packet];
        [self maybeDequeueSend];
    }});
}

- (void)setSendFilter:(GCDAsyncUdpSocketSendFilterBlock)filterBlock withQueue:(dispatch_queue_t)filterQueue
{
    [self setSendFilter:filterBlock withQueue:filterQueue isAsynchronous:YES];
}

- (void)setSendFilter:(GCDAsyncUdpSocketSendFilterBlock)filterBlock
            withQueue:(dispatch_queue_t)filterQueue
       isAsynchronous:(BOOL)isAsynchronous
{
    GCDAsyncUdpSocketSendFilterBlock newFilterBlock = NULL;
    dispatch_queue_t newFilterQueue = NULL;
    
    if (filterBlock)
    {
        NSAssert(filterQueue, @"Must provide a dispatch_queue in which to run the filter block.");
        
        newFilterBlock = [filterBlock copy];
        newFilterQueue = filterQueue;
#if !OS_OBJECT_USE_OBJC
        dispatch_retain(newFilterQueue);
#endif
    }
    
    dispatch_block_t block = ^{
        
#if !OS_OBJECT_USE_OBJC
        if (sendFilterQueue) dispatch_release(sendFilterQueue);
#endif
        
        sendFilterBlock = newFilterBlock;
        sendFilterQueue = newFilterQueue;
        sendFilterAsync = isAsynchronous;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_async(socketQueue, block);
}

- (void)maybeDequeueSend
{
    LogTrace();
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    
    // If we don't have a send operation already in progress
    if (currentSend == nil)
    {
        // Create the sockets if needed
        if ((flags & kDidCreateSockets) == 0)
        {
            NSError *err = nil;
            if (![self createSockets:&err])
            {
                [self closeWithError:err];
                return;
            }
        }
        
        while ([sendQueue count] > 0)
        {
            // Dequeue the next object in the queue
            currentSend = [sendQueue objectAtIndex:0];
            [sendQueue removeObjectAtIndex:0];
            
            if ([currentSend isKindOfClass:[GCDAsyncUdpSpecialPacket class]])
            {
                [self maybeConnect];
                
                return; // The maybeConnect method, if it connects, will invoke this method again
            }
            else if (currentSend->resolveError)
            {
                // Notify delegate
                [self notifyDidNotSendDataWithTag:currentSend->tag dueToError:currentSend->resolveError];
                
                // Clear currentSend
                currentSend = nil;
                
                continue;
            }
            else
            {
                // Start preprocessing checks on the send packet
                [self doPreSend];
                
                break;
            }
        }
        
        if ((currentSend == nil) && (flags & kCloseAfterSends))
        {
            [self closeWithError:nil];
        }
    }
}

/**
 * This method is called after a sendPacket has been dequeued.
 * It performs various preprocessing checks on the packet,
 * and queries the sendFilter (if set) to determine if the packet can be sent.
 *
 * If the packet passes all checks, it will be passed on to the doSend method.
 **/
- (void)doPreSend
{
    LogTrace();
    
    //
    // 1. Check for problems with send packet
    //
    
    BOOL waitingForResolve = NO;
    NSError *error = nil;
    
    if (flags & kDidConnect)
    {
        // Connected socket
        
        if (currentSend->resolveInProgress || currentSend->resolvedAddresses || currentSend->resolveError)
        {
            NSString *msg = @"Cannot specify destination of packet for connected socket";
            error = [self badConfigError:msg];
        }
        else
        {
            currentSend->address = cachedConnectedAddress;
            currentSend->addressFamily = cachedConnectedFamily;
        }
    }
    else
    {
        // Non-Connected socket
        
        if (currentSend->resolveInProgress)
        {
            // We're waiting for the packet's destination to be resolved.
            waitingForResolve = YES;
        }
        else if (currentSend->resolveError)
        {
            error = currentSend->resolveError;
        }
        else if (currentSend->address == nil)
        {
            if (currentSend->resolvedAddresses == nil)
            {
                NSString *msg = @"You must specify destination of packet for a non-connected socket";
                error = [self badConfigError:msg];
            }
            else
            {
                // Pick the proper address to use (out of possibly several resolved addresses)
                
                NSData *address = nil;
                int addressFamily = AF_UNSPEC;
                
                addressFamily = [self getAddress:&address error:&error fromAddresses:currentSend->resolvedAddresses];
                
                currentSend->address = address;
                currentSend->addressFamily = addressFamily;
            }
        }
    }
    
    if (waitingForResolve)
    {
        // We're waiting for the packet's destination to be resolved.
        
        LogVerbose(@"currentSend - waiting for address resolve");
        
        if (flags & kSock4CanAcceptBytes) {
            [self suspendSend4Source];
        }
        if (flags & kSock6CanAcceptBytes) {
            [self suspendSend6Source];
        }
        
        return;
    }
    
    if (error)
    {
        // Unable to send packet due to some error.
        // Notify delegate and move on.
        
        [self notifyDidNotSendDataWithTag:currentSend->tag dueToError:error];
        [self endCurrentSend];
        [self maybeDequeueSend];
        
        return;
    }
    
    //
    // 2. Query sendFilter (if applicable)
    //
    
    if (sendFilterBlock && sendFilterQueue)
    {
        // Query sendFilter
        
        if (sendFilterAsync)
        {
            // Scenario 1 of 3 - Need to asynchronously query sendFilter
            
            currentSend->filterInProgress = YES;
            GCDAsyncUdpSendPacket *sendPacket = currentSend;
            
            dispatch_async(sendFilterQueue, ^{ @autoreleasepool {
                
                BOOL allowed = sendFilterBlock(sendPacket->buffer, sendPacket->address, sendPacket->tag);
                
                dispatch_async(socketQueue, ^{ @autoreleasepool {
                    
                    sendPacket->filterInProgress = NO;
                    if (sendPacket == currentSend)
                    {
                        if (allowed)
                        {
                            [self doSend];
                        }
                        else
                        {
                            LogVerbose(@"currentSend - silently dropped by sendFilter");
                            
                            [self notifyDidSendDataWithTag:currentSend->tag];
                            [self endCurrentSend];
                            [self maybeDequeueSend];
                        }
                    }
                }});
            }});
        }
        else
        {
            // Scenario 2 of 3 - Need to synchronously query sendFilter
            
            __block BOOL allowed = YES;
            
            dispatch_sync(sendFilterQueue, ^{ @autoreleasepool {
                
                allowed = sendFilterBlock(currentSend->buffer, currentSend->address, currentSend->tag);
            }});
            
            if (allowed)
            {
                [self doSend];
            }
            else
            {
                LogVerbose(@"currentSend - silently dropped by sendFilter");
                
                [self notifyDidSendDataWithTag:currentSend->tag];
                [self endCurrentSend];
                [self maybeDequeueSend];
            }
        }
    }
    else // if (!sendFilterBlock || !sendFilterQueue)
    {
        // Scenario 3 of 3 - No sendFilter. Just go straight into sending.
        
        [self doSend];
    }
}

/**
 * This method performs the actual sending of data in the currentSend packet.
 * It should only be called if the
 **/
- (void)doSend
{
    LogTrace();
    
    NSAssert(currentSend != nil, @"Invalid logic");
    
    // Perform the actual send
    
    ssize_t result = 0;
    
    if (flags & kDidConnect)
    {
        // Connected socket
        
        const void *buffer = [currentSend->buffer bytes];
        size_t length = (size_t)[currentSend->buffer length];
        
        if (currentSend->addressFamily == AF_INET)
        {
            result = send(socket4FD, buffer, length, 0);
            LogVerbose(@"send(socket4FD) = %d", result);
        }
        else
        {
            result = send(socket6FD, buffer, length, 0);
            LogVerbose(@"send(socket6FD) = %d", result);
        }
    }
    else
    {
        // Non-Connected socket
        
        const void *buffer = [currentSend->buffer bytes];
        size_t length = (size_t)[currentSend->buffer length];
        
        const void *dst  = [currentSend->address bytes];
        socklen_t dstSize = (socklen_t)[currentSend->address length];
        
        if (currentSend->addressFamily == AF_INET)
        {
            result = sendto(socket4FD, buffer, length, 0, dst, dstSize);
            LogVerbose(@"sendto(socket4FD) = %d", result);
        }
        else
        {
            result = sendto(socket6FD, buffer, length, 0, dst, dstSize);
            LogVerbose(@"sendto(socket6FD) = %d", result);
        }
    }
    
    // If the socket wasn't bound before, it is now
    
    if ((flags & kDidBind) == 0)
    {
        flags |= kDidBind;
    }
    
    // Check the results.
    //
    // From the send() & sendto() manpage:
    //
    // Upon successful completion, the number of bytes which were sent is returned.
    // Otherwise, -1 is returned and the global variable errno is set to indicate the error.
    
    BOOL waitingForSocket = NO;
    NSError *socketError = nil;
    
    if (result == 0)
    {
        waitingForSocket = YES;
    }
    else if (result < 0)
    {
        if (errno == EAGAIN)
            waitingForSocket = YES;
        else
            socketError = [self errnoErrorWithReason:@"Error in send() function."];
    }
    
    if (waitingForSocket)
    {
        // Not enough room in the underlying OS socket send buffer.
        // Wait for a notification of available space.
        
        LogVerbose(@"currentSend - waiting for socket");
        
        if (!(flags & kSock4CanAcceptBytes)) {
            [self resumeSend4Source];
        }
        if (!(flags & kSock6CanAcceptBytes)) {
            [self resumeSend6Source];
        }
        
        if ((sendTimer == NULL) && (currentSend->timeout >= 0.0))
        {
            // Unable to send packet right away.
            // Start timer to timeout the send operation.
            
            [self setupSendTimerWithTimeout:currentSend->timeout];
        }
    }
    else if (socketError)
    {
        [self closeWithError:socketError];
    }
    else // done
    {
        [self notifyDidSendDataWithTag:currentSend->tag];
        [self endCurrentSend];
        [self maybeDequeueSend];
    }
}

/**
 * Releases all resources associated with the currentSend.
 **/
- (void)endCurrentSend
{
    if (sendTimer)
    {
        dispatch_source_cancel(sendTimer);
#if !OS_OBJECT_USE_OBJC
        dispatch_release(sendTimer);
#endif
        sendTimer = NULL;
    }
    
    currentSend = nil;
}

/**
 * Performs the operations to timeout the current send operation, and move on.
 **/
- (void)doSendTimeout
{
    LogTrace();
    
    [self notifyDidNotSendDataWithTag:currentSend->tag dueToError:[self sendTimeoutError]];
    [self endCurrentSend];
    [self maybeDequeueSend];
}

/**
 * Sets up a timer that fires to timeout the current send operation.
 * This method should only be called once per send packet.
 **/
- (void)setupSendTimerWithTimeout:(NSTimeInterval)timeout
{
    NSAssert(sendTimer == NULL, @"Invalid logic");
    NSAssert(timeout >= 0.0, @"Invalid logic");
    
    LogTrace();
    
    sendTimer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, socketQueue);
    
    dispatch_source_set_event_handler(sendTimer, ^{ @autoreleasepool {
        
        [self doSendTimeout];
    }});
    
    dispatch_time_t tt = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(timeout * NSEC_PER_SEC));
    
    dispatch_source_set_timer(sendTimer, tt, DISPATCH_TIME_FOREVER, 0);
    dispatch_resume(sendTimer);
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Receiving
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

- (BOOL)receiveOnce:(NSError **)errPtr
{
    LogTrace();
    
    __block BOOL result = NO;
    __block NSError *err = nil;
    
    dispatch_block_t block = ^{
        
        if ((flags & kReceiveOnce) == 0)
        {
            if ((flags & kDidCreateSockets) == 0)
            {
                NSString *msg = @"Must bind socket before you can receive data. "
                @"You can do this explicitly via bind, or implicitly via connect or by sending data.";
                
                err = [self badConfigError:msg];
                return_from_block;
            }
            
            flags |=  kReceiveOnce;       // Enable
            flags &= ~kReceiveContinuous; // Disable
            
            dispatch_async(socketQueue, ^{ @autoreleasepool {
                
                [self doReceive];
            }});
        }
        
        result = YES;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    if (err)
        LogError(@"Error in beginReceiving: %@", err);
    
    if (errPtr)
        *errPtr = err;
    
    return result;
}

- (BOOL)beginReceiving:(NSError **)errPtr
{
    LogTrace();
    
    __block BOOL result = NO;
    __block NSError *err = nil;
    
    dispatch_block_t block = ^{
        
        if ((flags & kReceiveContinuous) == 0)
        {
            if ((flags & kDidCreateSockets) == 0)
            {
                NSString *msg = @"Must bind socket before you can receive data. "
                @"You can do this explicitly via bind, or implicitly via connect or by sending data.";
                
                err = [self badConfigError:msg];
                return_from_block;
            }
            
            flags |= kReceiveContinuous; // Enable
            flags &= ~kReceiveOnce;      // Disable
            
            dispatch_async(socketQueue, ^{ @autoreleasepool {
                
                [self doReceive];
            }});
        }
        
        result = YES;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
    
    if (err)
        LogError(@"Error in beginReceiving: %@", err);
    
    if (errPtr)
        *errPtr = err;
    
    return result;
}

- (void)pauseReceiving
{
    LogTrace();
    
    dispatch_block_t block = ^{
        
        flags &= ~kReceiveOnce;       // Disable
        flags &= ~kReceiveContinuous; // Disable
        
        if (socket4FDBytesAvailable > 0) {
            [self suspendReceive4Source];
        }
        if (socket6FDBytesAvailable > 0) {
            [self suspendReceive6Source];
        }
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_async(socketQueue, block);
}

- (void)setReceiveFilter:(GCDAsyncUdpSocketReceiveFilterBlock)filterBlock withQueue:(dispatch_queue_t)filterQueue
{
    [self setReceiveFilter:filterBlock withQueue:filterQueue isAsynchronous:YES];
}

- (void)setReceiveFilter:(GCDAsyncUdpSocketReceiveFilterBlock)filterBlock
               withQueue:(dispatch_queue_t)filterQueue
          isAsynchronous:(BOOL)isAsynchronous
{
    GCDAsyncUdpSocketReceiveFilterBlock newFilterBlock = NULL;
    dispatch_queue_t newFilterQueue = NULL;
    
    if (filterBlock)
    {
        NSAssert(filterQueue, @"Must provide a dispatch_queue in which to run the filter block.");
        
        newFilterBlock = [filterBlock copy];
        newFilterQueue = filterQueue;
#if !OS_OBJECT_USE_OBJC
        dispatch_retain(newFilterQueue);
#endif
    }
    
    dispatch_block_t block = ^{
        
#if !OS_OBJECT_USE_OBJC
        if (receiveFilterQueue) dispatch_release(receiveFilterQueue);
#endif
        
        receiveFilterBlock = newFilterBlock;
        receiveFilterQueue = newFilterQueue;
        receiveFilterAsync = isAsynchronous;
    };
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_async(socketQueue, block);
}

- (void)doReceive
{
    LogTrace();
    
    if ((flags & (kReceiveOnce | kReceiveContinuous)) == 0)
    {
        LogVerbose(@"Receiving is paused...");
        
        if (socket4FDBytesAvailable > 0) {
            [self suspendReceive4Source];
        }
        if (socket6FDBytesAvailable > 0) {
            [self suspendReceive6Source];
        }
        
        return;
    }
    
    if ((flags & kReceiveOnce) && (pendingFilterOperations > 0))
    {
        LogVerbose(@"Receiving is temporarily paused (pending filter operations)...");
        
        if (socket4FDBytesAvailable > 0) {
            [self suspendReceive4Source];
        }
        if (socket6FDBytesAvailable > 0) {
            [self suspendReceive6Source];
        }
        
        return;
    }
    
    if ((socket4FDBytesAvailable == 0) && (socket6FDBytesAvailable == 0))
    {
        LogVerbose(@"No data available to receive...");
        
        if (socket4FDBytesAvailable == 0) {
            [self resumeReceive4Source];
        }
        if (socket6FDBytesAvailable == 0) {
            [self resumeReceive6Source];
        }
        
        return;
    }
    
    // Figure out if we should receive on socket4 or socket6
    
    BOOL doReceive4;
    
    if (flags & kDidConnect)
    {
        // Connected socket
        
        doReceive4 = (socket4FD != SOCKET_NULL);
    }
    else
    {
        // Non-Connected socket
        
        if (socket4FDBytesAvailable > 0)
        {
            if (socket6FDBytesAvailable > 0)
            {
                // Bytes available on socket4 & socket6
                
                doReceive4 = (flags & kFlipFlop) ? YES : NO;
                
                flags ^= kFlipFlop; // flags = flags xor kFlipFlop; (toggle flip flop bit)
            }
            else {
                // Bytes available on socket4, but not socket6
                doReceive4 = YES;
            }
        }
        else {
            // Bytes available on socket6, but not socket4
            doReceive4 = NO;
        }
    }
    
    // Perform socket IO
    
    ssize_t result = 0;
    
    NSData *data = nil;
    NSData *addr4 = nil;
    NSData *addr6 = nil;
    
    if (doReceive4)
    {
        NSAssert(socket4FDBytesAvailable > 0, @"Invalid logic");
        LogVerbose(@"Receiving on IPv4");
        
        struct sockaddr_in sockaddr4;
        socklen_t sockaddr4len = sizeof(sockaddr4);
        
        // #222: GCD does not necessarily return the size of an entire UDP packet
        // from dispatch_source_get_data(), so we must use the maximum packet size.
        size_t bufSize = max4ReceiveSize;
        void *buf = malloc(bufSize);
        
        result = recvfrom(socket4FD, buf, bufSize, 0, (struct sockaddr *)&sockaddr4, &sockaddr4len);
        LogVerbose(@"recvfrom(socket4FD) = %i", (int)result);
        
        if (result > 0)
        {
            if ((size_t)result >= socket4FDBytesAvailable)
                socket4FDBytesAvailable = 0;
            else
                socket4FDBytesAvailable -= result;
            
            if ((size_t)result != bufSize) {
                buf = realloc(buf, result);
            }
            
            data = [NSData dataWithBytesNoCopy:buf length:result freeWhenDone:YES];
            addr4 = [NSData dataWithBytes:&sockaddr4 length:sockaddr4len];
        }
        else
        {
            LogVerbose(@"recvfrom(socket4FD) = %@", [self errnoError]);
            socket4FDBytesAvailable = 0;
            free(buf);
        }
    }
    else
    {
        NSAssert(socket6FDBytesAvailable > 0, @"Invalid logic");
        LogVerbose(@"Receiving on IPv6");
        
        struct sockaddr_in6 sockaddr6;
        socklen_t sockaddr6len = sizeof(sockaddr6);
        
        // #222: GCD does not necessarily return the size of an entire UDP packet
        // from dispatch_source_get_data(), so we must use the maximum packet size.
        size_t bufSize = max6ReceiveSize;
        void *buf = malloc(bufSize);
        
        result = recvfrom(socket6FD, buf, bufSize, 0, (struct sockaddr *)&sockaddr6, &sockaddr6len);
        LogVerbose(@"recvfrom(socket6FD) -> %i", (int)result);
        
        if (result > 0)
        {
            if ((size_t)result >= socket6FDBytesAvailable)
                socket6FDBytesAvailable = 0;
            else
                socket6FDBytesAvailable -= result;
            
            if ((size_t)result != bufSize) {
                buf = realloc(buf, result);
            }
            
            data = [NSData dataWithBytesNoCopy:buf length:result freeWhenDone:YES];
            addr6 = [NSData dataWithBytes:&sockaddr6 length:sockaddr6len];
        }
        else
        {
            LogVerbose(@"recvfrom(socket6FD) = %@", [self errnoError]);
            socket6FDBytesAvailable = 0;
            free(buf);
        }
    }
    
    
    BOOL waitingForSocket = NO;
    BOOL notifiedDelegate = NO;
    BOOL ignored = NO;
    
    NSError *socketError = nil;
    
    if (result == 0)
    {
        waitingForSocket = YES;
    }
    else if (result < 0)
    {
        if (errno == EAGAIN)
            waitingForSocket = YES;
        else
            socketError = [self errnoErrorWithReason:@"Error in recvfrom() function"];
    }
    else
    {
        if (flags & kDidConnect)
        {
            if (addr4 && ![self isConnectedToAddress4:addr4])
                ignored = YES;
            if (addr6 && ![self isConnectedToAddress6:addr6])
                ignored = YES;
        }
        
        NSData *addr = (addr4 != nil) ? addr4 : addr6;
        
        if (!ignored)
        {
            if (receiveFilterBlock && receiveFilterQueue)
            {
                // Run data through filter, and if approved, notify delegate
                
                __block id filterContext = nil;
                __block BOOL allowed = NO;
                
                if (receiveFilterAsync)
                {
                    pendingFilterOperations++;
                    dispatch_async(receiveFilterQueue, ^{ @autoreleasepool {
                        
                        allowed = receiveFilterBlock(data, addr, &filterContext);
                        
                        // Transition back to socketQueue to get the current delegate / delegateQueue
                        dispatch_async(socketQueue, ^{ @autoreleasepool {
                            
                            pendingFilterOperations--;
                            
                            if (allowed)
                            {
                                [self notifyDidReceiveData:data fromAddress:addr withFilterContext:filterContext];
                            }
                            else
                            {
                                LogVerbose(@"received packet silently dropped by receiveFilter");
                            }
                            
                            if (flags & kReceiveOnce)
                            {
                                if (allowed)
                                {
                                    // The delegate has been notified,
                                    // so our receive once operation has completed.
                                    flags &= ~kReceiveOnce;
                                }
                                else if (pendingFilterOperations == 0)
                                {
                                    // All pending filter operations have completed,
                                    // and none were allowed through.
                                    // Our receive once operation hasn't completed yet.
                                    [self doReceive];
                                }
                            }
                        }});
                    }});
                }
                else // if (!receiveFilterAsync)
                {
                    dispatch_sync(receiveFilterQueue, ^{ @autoreleasepool {
                        
                        allowed = receiveFilterBlock(data, addr, &filterContext);
                    }});
                    
                    if (allowed)
                    {
                        [self notifyDidReceiveData:data fromAddress:addr withFilterContext:filterContext];
                        notifiedDelegate = YES;
                    }
                    else
                    {
                        LogVerbose(@"received packet silently dropped by receiveFilter");
                        ignored = YES;
                    }
                }
            }
            else // if (!receiveFilterBlock || !receiveFilterQueue)
            {
                [self notifyDidReceiveData:data fromAddress:addr withFilterContext:nil];
                notifiedDelegate = YES;
            }
        }
    }
    
    if (waitingForSocket)
    {
        // Wait for a notification of available data.
        
        if (socket4FDBytesAvailable == 0) {
            [self resumeReceive4Source];
        }
        if (socket6FDBytesAvailable == 0) {
            [self resumeReceive6Source];
        }
    }
    else if (socketError)
    {
        [self closeWithError:socketError];
    }
    else
    {
        if (flags & kReceiveContinuous)
        {
            // Continuous receive mode
            [self doReceive];
        }
        else
        {
            // One-at-a-time receive mode
            if (notifiedDelegate)
            {
                // The delegate has been notified (no set filter).
                // So our receive once operation has completed.
                flags &= ~kReceiveOnce;
            }
            else if (ignored)
            {
                [self doReceive];
            }
            else
            {
                // Waiting on asynchronous receive filter...
            }
        }
    }
}

- (void)doReceiveEOF
{
    LogTrace();
    
    [self closeWithError:[self socketClosedError]];
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Closing
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

- (void)closeWithError:(NSError *)error
{
    LogVerbose(@"closeWithError: %@", error);
    
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    
    if (currentSend) [self endCurrentSend];
    
    [sendQueue removeAllObjects];
    
    // If a socket has been created, we should notify the delegate.
    BOOL shouldCallDelegate = (flags & kDidCreateSockets) ? YES : NO;
    
    // Close all sockets, send/receive sources, cfstreams, etc
#if TARGET_OS_IPHONE
    [self removeStreamsFromRunLoop];
    [self closeReadAndWriteStreams];
#endif
    [self closeSockets];
    
    // Clear all flags (config remains as is)
    flags = 0;
    
    if (shouldCallDelegate)
    {
        [self notifyDidCloseWithError:error];
    }
}

- (void)close
{
    LogTrace();
    
    dispatch_block_t block = ^{ @autoreleasepool {
        
        [self closeWithError:nil];
    }};
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
}

- (void)closeAfterSending
{
    LogTrace();
    
    dispatch_block_t block = ^{ @autoreleasepool {
        
        flags |= kCloseAfterSends;
        
        if (currentSend == nil && [sendQueue count] == 0)
        {
            [self closeWithError:nil];
        }
    }};
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_async(socketQueue, block);
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark CFStream
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

#if TARGET_OS_IPHONE

static NSThread *listenerThread;

+ (void)ignore:(id)_
{}

+ (void)startListenerThreadIfNeeded
{
    static dispatch_once_t predicate;
    dispatch_once(&predicate, ^{
        
        listenerThread = [[NSThread alloc] initWithTarget:self
                                                 selector:@selector(listenerThread)
                                                   object:nil];
        [listenerThread start];
    });
}

+ (void)listenerThread
{
    @autoreleasepool {
        
        [[NSThread currentThread] setName:GCDAsyncUdpSocketThreadName];
        
        LogInfo(@"ListenerThread: Started");
        
        // We can't run the run loop unless it has an associated input source or a timer.
        // So we'll just create a timer that will never fire - unless the server runs for a decades.
        [NSTimer scheduledTimerWithTimeInterval:[[NSDate distantFuture] timeIntervalSinceNow]
                                         target:self
                                       selector:@selector(ignore:)
                                       userInfo:nil
                                        repeats:YES];
        
        [[NSRunLoop currentRunLoop] run];
        
        LogInfo(@"ListenerThread: Stopped");
    }
}

+ (void)addStreamListener:(GCDAsyncUdpSocket *)asyncUdpSocket
{
    LogTrace();
    NSAssert([NSThread currentThread] == listenerThread, @"Invoked on wrong thread");
    
    CFRunLoopRef runLoop = CFRunLoopGetCurrent();
    
    if (asyncUdpSocket->readStream4)
        CFReadStreamScheduleWithRunLoop(asyncUdpSocket->readStream4, runLoop, kCFRunLoopDefaultMode);
    
    if (asyncUdpSocket->readStream6)
        CFReadStreamScheduleWithRunLoop(asyncUdpSocket->readStream6, runLoop, kCFRunLoopDefaultMode);
    
    if (asyncUdpSocket->writeStream4)
        CFWriteStreamScheduleWithRunLoop(asyncUdpSocket->writeStream4, runLoop, kCFRunLoopDefaultMode);
    
    if (asyncUdpSocket->writeStream6)
        CFWriteStreamScheduleWithRunLoop(asyncUdpSocket->writeStream6, runLoop, kCFRunLoopDefaultMode);
}

+ (void)removeStreamListener:(GCDAsyncUdpSocket *)asyncUdpSocket
{
    LogTrace();
    NSAssert([NSThread currentThread] == listenerThread, @"Invoked on wrong thread");
    
    CFRunLoopRef runLoop = CFRunLoopGetCurrent();
    
    if (asyncUdpSocket->readStream4)
        CFReadStreamUnscheduleFromRunLoop(asyncUdpSocket->readStream4, runLoop, kCFRunLoopDefaultMode);
    
    if (asyncUdpSocket->readStream6)
        CFReadStreamUnscheduleFromRunLoop(asyncUdpSocket->readStream6, runLoop, kCFRunLoopDefaultMode);
    
    if (asyncUdpSocket->writeStream4)
        CFWriteStreamUnscheduleFromRunLoop(asyncUdpSocket->writeStream4, runLoop, kCFRunLoopDefaultMode);
    
    if (asyncUdpSocket->writeStream6)
        CFWriteStreamUnscheduleFromRunLoop(asyncUdpSocket->writeStream6, runLoop, kCFRunLoopDefaultMode);
}

static void CFReadStreamCallback(CFReadStreamRef stream, CFStreamEventType type, void *pInfo)
{
    @autoreleasepool {
        GCDAsyncUdpSocket *asyncUdpSocket = (__bridge GCDAsyncUdpSocket *)pInfo;
        
        switch(type)
        {
            case kCFStreamEventOpenCompleted:
            {
                LogCVerbose(@"CFReadStreamCallback - Open");
                break;
            }
            case kCFStreamEventHasBytesAvailable:
            {
                LogCVerbose(@"CFReadStreamCallback - HasBytesAvailable");
                break;
            }
            case kCFStreamEventErrorOccurred:
            case kCFStreamEventEndEncountered:
            {
                NSError *error = (__bridge_transfer NSError *)CFReadStreamCopyError(stream);
                if (error == nil && type == kCFStreamEventEndEncountered)
                {
                    error = [asyncUdpSocket socketClosedError];
                }
                
                dispatch_async(asyncUdpSocket->socketQueue, ^{ @autoreleasepool {
                    
                    LogCVerbose(@"CFReadStreamCallback - %@",
                                (type == kCFStreamEventErrorOccurred) ? @"Error" : @"EndEncountered");
                    
                    if (stream != asyncUdpSocket->readStream4 &&
                        stream != asyncUdpSocket->readStream6  )
                    {
                        LogCVerbose(@"CFReadStreamCallback - Ignored");
                        return_from_block;
                    }
                    
                    [asyncUdpSocket closeWithError:error];
                    
                }});
                
                break;
            }
            default:
            {
                LogCError(@"CFReadStreamCallback - UnknownType: %i", (int)type);
            }
        }
    }
}

static void CFWriteStreamCallback(CFWriteStreamRef stream, CFStreamEventType type, void *pInfo)
{
    @autoreleasepool {
        GCDAsyncUdpSocket *asyncUdpSocket = (__bridge GCDAsyncUdpSocket *)pInfo;
        
        switch(type)
        {
            case kCFStreamEventOpenCompleted:
            {
                LogCVerbose(@"CFWriteStreamCallback - Open");
                break;
            }
            case kCFStreamEventCanAcceptBytes:
            {
                LogCVerbose(@"CFWriteStreamCallback - CanAcceptBytes");
                break;
            }
            case kCFStreamEventErrorOccurred:
            case kCFStreamEventEndEncountered:
            {
                NSError *error = (__bridge_transfer NSError *)CFWriteStreamCopyError(stream);
                if (error == nil && type == kCFStreamEventEndEncountered)
                {
                    error = [asyncUdpSocket socketClosedError];
                }
                
                dispatch_async(asyncUdpSocket->socketQueue, ^{ @autoreleasepool {
                    
                    LogCVerbose(@"CFWriteStreamCallback - %@",
                                (type == kCFStreamEventErrorOccurred) ? @"Error" : @"EndEncountered");
                    
                    if (stream != asyncUdpSocket->writeStream4 &&
                        stream != asyncUdpSocket->writeStream6  )
                    {
                        LogCVerbose(@"CFWriteStreamCallback - Ignored");
                        return_from_block;
                    }
                    
                    [asyncUdpSocket closeWithError:error];
                    
                }});
                
                break;
            }
            default:
            {
                LogCError(@"CFWriteStreamCallback - UnknownType: %i", (int)type);
            }
        }
    }
}

- (BOOL)createReadAndWriteStreams:(NSError **)errPtr
{
    LogTrace();
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    
    NSError *err = nil;
    
    if (readStream4 || writeStream4 || readStream6 || writeStream6)
    {
        // Streams already created
        return YES;
    }
    
    if (socket4FD == SOCKET_NULL && socket6FD == SOCKET_NULL)
    {
        err = [self otherError:@"Cannot create streams without a file descriptor"];
        goto Failed;
    }
    
    // Create streams
    
    LogVerbose(@"Creating read and write stream(s)...");
    
    if (socket4FD != SOCKET_NULL)
    {
        CFStreamCreatePairWithSocket(NULL, (CFSocketNativeHandle)socket4FD, &readStream4, &writeStream4);
        if (!readStream4 || !writeStream4)
        {
            err = [self otherError:@"Error in CFStreamCreatePairWithSocket() [IPv4]"];
            goto Failed;
        }
    }
    
    if (socket6FD != SOCKET_NULL)
    {
        CFStreamCreatePairWithSocket(NULL, (CFSocketNativeHandle)socket6FD, &readStream6, &writeStream6);
        if (!readStream6 || !writeStream6)
        {
            err = [self otherError:@"Error in CFStreamCreatePairWithSocket() [IPv6]"];
            goto Failed;
        }
    }
    
    // Ensure the CFStream's don't close our underlying socket
    
    CFReadStreamSetProperty(readStream4, kCFStreamPropertyShouldCloseNativeSocket, kCFBooleanFalse);
    CFWriteStreamSetProperty(writeStream4, kCFStreamPropertyShouldCloseNativeSocket, kCFBooleanFalse);
    
    CFReadStreamSetProperty(readStream6, kCFStreamPropertyShouldCloseNativeSocket, kCFBooleanFalse);
    CFWriteStreamSetProperty(writeStream6, kCFStreamPropertyShouldCloseNativeSocket, kCFBooleanFalse);
    
    return YES;
    
Failed:
    if (readStream4)
    {
        CFReadStreamClose(readStream4);
        CFRelease(readStream4);
        readStream4 = NULL;
    }
    if (writeStream4)
    {
        CFWriteStreamClose(writeStream4);
        CFRelease(writeStream4);
        writeStream4 = NULL;
    }
    if (readStream6)
    {
        CFReadStreamClose(readStream6);
        CFRelease(readStream6);
        readStream6 = NULL;
    }
    if (writeStream6)
    {
        CFWriteStreamClose(writeStream6);
        CFRelease(writeStream6);
        writeStream6 = NULL;
    }
    
    if (errPtr)
        *errPtr = err;
    
    return NO;
}

- (BOOL)registerForStreamCallbacks:(NSError **)errPtr
{
    LogTrace();
    
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    NSAssert(readStream4 || writeStream4 || readStream6 || writeStream6, @"Read/Write streams are null");
    
    NSError *err = nil;
    
    streamContext.version = 0;
    streamContext.info = (__bridge void *)self;
    streamContext.retain = nil;
    streamContext.release = nil;
    streamContext.copyDescription = nil;
    
    CFOptionFlags readStreamEvents = kCFStreamEventErrorOccurred | kCFStreamEventEndEncountered;
    CFOptionFlags writeStreamEvents = kCFStreamEventErrorOccurred | kCFStreamEventEndEncountered;
    
    //	readStreamEvents  |= (kCFStreamEventOpenCompleted | kCFStreamEventHasBytesAvailable);
    //	writeStreamEvents |= (kCFStreamEventOpenCompleted | kCFStreamEventCanAcceptBytes);
    
    if (socket4FD != SOCKET_NULL)
    {
        if (readStream4 == NULL || writeStream4 == NULL)
        {
            err = [self otherError:@"Read/Write stream4 is null"];
            goto Failed;
        }
        
        BOOL r1 = CFReadStreamSetClient(readStream4, readStreamEvents, &CFReadStreamCallback, &streamContext);
        BOOL r2 = CFWriteStreamSetClient(writeStream4, writeStreamEvents, &CFWriteStreamCallback, &streamContext);
        
        if (!r1 || !r2)
        {
            err = [self otherError:@"Error in CFStreamSetClient(), [IPv4]"];
            goto Failed;
        }
    }
    
    if (socket6FD != SOCKET_NULL)
    {
        if (readStream6 == NULL || writeStream6 == NULL)
        {
            err = [self otherError:@"Read/Write stream6 is null"];
            goto Failed;
        }
        
        BOOL r1 = CFReadStreamSetClient(readStream6, readStreamEvents, &CFReadStreamCallback, &streamContext);
        BOOL r2 = CFWriteStreamSetClient(writeStream6, writeStreamEvents, &CFWriteStreamCallback, &streamContext);
        
        if (!r1 || !r2)
        {
            err = [self otherError:@"Error in CFStreamSetClient() [IPv6]"];
            goto Failed;
        }
    }
    
    return YES;
    
Failed:
    if (readStream4) {
        CFReadStreamSetClient(readStream4, kCFStreamEventNone, NULL, NULL);
    }
    if (writeStream4) {
        CFWriteStreamSetClient(writeStream4, kCFStreamEventNone, NULL, NULL);
    }
    if (readStream6) {
        CFReadStreamSetClient(readStream6, kCFStreamEventNone, NULL, NULL);
    }
    if (writeStream6) {
        CFWriteStreamSetClient(writeStream6, kCFStreamEventNone, NULL, NULL);
    }
    
    if (errPtr) *errPtr = err;
    return NO;
}

- (BOOL)addStreamsToRunLoop:(NSError **)errPtr
{
    LogTrace();
    
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    NSAssert(readStream4 || writeStream4 || readStream6 || writeStream6, @"Read/Write streams are null");
    
    if (!(flags & kAddedStreamListener))
    {
        [[self class] startListenerThreadIfNeeded];
        [[self class] performSelector:@selector(addStreamListener:)
                             onThread:listenerThread
                           withObject:self
                        waitUntilDone:YES];
        
        flags |= kAddedStreamListener;
    }
    
    return YES;
}

- (BOOL)openStreams:(NSError **)errPtr
{
    LogTrace();
    
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    NSAssert(readStream4 || writeStream4 || readStream6 || writeStream6, @"Read/Write streams are null");
    
    NSError *err = nil;
    
    if (socket4FD != SOCKET_NULL)
    {
        BOOL r1 = CFReadStreamOpen(readStream4);
        BOOL r2 = CFWriteStreamOpen(writeStream4);
        
        if (!r1 || !r2)
        {
            err = [self otherError:@"Error in CFStreamOpen() [IPv4]"];
            goto Failed;
        }
    }
    
    if (socket6FD != SOCKET_NULL)
    {
        BOOL r1 = CFReadStreamOpen(readStream6);
        BOOL r2 = CFWriteStreamOpen(writeStream6);
        
        if (!r1 || !r2)
        {
            err = [self otherError:@"Error in CFStreamOpen() [IPv6]"];
            goto Failed;
        }
    }
    
    return YES;
    
Failed:
    if (errPtr) *errPtr = err;
    return NO;
}

- (void)removeStreamsFromRunLoop
{
    LogTrace();
    NSAssert(dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey), @"Must be dispatched on socketQueue");
    
    if (flags & kAddedStreamListener)
    {
        [[self class] performSelector:@selector(removeStreamListener:)
                             onThread:listenerThread
                           withObject:self
                        waitUntilDone:YES];
        
        flags &= ~kAddedStreamListener;
    }
}

- (void)closeReadAndWriteStreams
{
    LogTrace();
    
    if (readStream4)
    {
        CFReadStreamSetClient(readStream4, kCFStreamEventNone, NULL, NULL);
        CFReadStreamClose(readStream4);
        CFRelease(readStream4);
        readStream4 = NULL;
    }
    if (writeStream4)
    {
        CFWriteStreamSetClient(writeStream4, kCFStreamEventNone, NULL, NULL);
        CFWriteStreamClose(writeStream4);
        CFRelease(writeStream4);
        writeStream4 = NULL;
    }
    if (readStream6)
    {
        CFReadStreamSetClient(readStream6, kCFStreamEventNone, NULL, NULL);
        CFReadStreamClose(readStream6);
        CFRelease(readStream6);
        readStream6 = NULL;
    }
    if (writeStream6)
    {
        CFWriteStreamSetClient(writeStream6, kCFStreamEventNone, NULL, NULL);
        CFWriteStreamClose(writeStream6);
        CFRelease(writeStream6);
        writeStream6 = NULL;
    }
}

#endif

- (void)applicationWillEnterForeground:(NSNotification *)notification
{
    LogTrace();
    
    // If the application was backgrounded, then iOS may have shut down our sockets.
    // So we take a quick look to see if any of them received an EOF.
    
    dispatch_block_t block = ^{ @autoreleasepool {
        
        [self resumeReceive4Source];
        [self resumeReceive6Source];
    }};
    
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_async(socketQueue, block);
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Advanced
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

/**
 * See header file for big discussion of this method.
 **/
- (void)markSocketQueueTargetQueue:(dispatch_queue_t)socketNewTargetQueue
{
    void *nonNullUnusedPointer = (__bridge void *)self;
    dispatch_queue_set_specific(socketNewTargetQueue, IsOnSocketQueueOrTargetQueueKey, nonNullUnusedPointer, NULL);
}

/**
 * See header file for big discussion of this method.
 **/
- (void)unmarkSocketQueueTargetQueue:(dispatch_queue_t)socketOldTargetQueue
{
    dispatch_queue_set_specific(socketOldTargetQueue, IsOnSocketQueueOrTargetQueueKey, NULL, NULL);
}

- (void)performBlock:(dispatch_block_t)block
{
    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
        block();
    else
        dispatch_sync(socketQueue, block);
}

- (int)socketFD
{
    if (! dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
    {
        LogWarn(@"%@: %@ - Method only available from within the context of a performBlock: invocation",
                THIS_FILE, THIS_METHOD);
        return SOCKET_NULL;
    }
    
    if (socket4FD != SOCKET_NULL)
        return socket4FD;
    else
        return socket6FD;
}

- (int)socket4FD
{
    if (! dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
    {
        LogWarn(@"%@: %@ - Method only available from within the context of a performBlock: invocation",
                THIS_FILE, THIS_METHOD);
        return SOCKET_NULL;
    }
    
    return socket4FD;
}

- (int)socket6FD
{
    if (! dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
    {
        LogWarn(@"%@: %@ - Method only available from within the context of a performBlock: invocation",
                THIS_FILE, THIS_METHOD);
        return SOCKET_NULL;
    }
    
    return socket6FD;
}

#if TARGET_OS_IPHONE

- (CFReadStreamRef)readStream
{
    if (! dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
    {
        LogWarn(@"%@: %@ - Method only available from within the context of a performBlock: invocation",
                THIS_FILE, THIS_METHOD);
        return NULL;
    }
    
    NSError *err = nil;
    if (![self createReadAndWriteStreams:&err])
    {
        LogError(@"Error creating CFStream(s): %@", err);
        return NULL;
    }
    
    // Todo...
    
    if (readStream4)
        return readStream4;
    else
        return readStream6;
}

- (CFWriteStreamRef)writeStream
{
    if (! dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
    {
        LogWarn(@"%@: %@ - Method only available from within the context of a performBlock: invocation",
                THIS_FILE, THIS_METHOD);
        return NULL;
    }
    
    NSError *err = nil;
    if (![self createReadAndWriteStreams:&err])
    {
        LogError(@"Error creating CFStream(s): %@", err);
        return NULL;
    }
    
    if (writeStream4)
        return writeStream4;
    else
        return writeStream6;
}

- (BOOL)enableBackgroundingOnSockets
{
    if (! dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
    {
        LogWarn(@"%@: %@ - Method only available from within the context of a performBlock: invocation",
                THIS_FILE, THIS_METHOD);
        return NO;
    }
    
    // Why is this commented out?
    // See comments below.
    
    //	NSError *err = nil;
    //	if (![self createReadAndWriteStreams:&err])
    //	{
    //		LogError(@"Error creating CFStream(s): %@", err);
    //		return NO;
    //	}
    //	
    //	LogVerbose(@"Enabling backgrouding on socket");
    //	
    //	BOOL r1, r2;
    //	
    //	if (readStream4 && writeStream4)
    //	{
    //		r1 = CFReadStreamSetProperty(readStream4, kCFStreamNetworkServiceType, kCFStreamNetworkServiceTypeVoIP);
    //		r2 = CFWriteStreamSetProperty(writeStream4, kCFStreamNetworkServiceType, kCFStreamNetworkServiceTypeVoIP);
    //		
    //		if (!r1 || !r2)
    //		{
    //			LogError(@"Error setting voip type (IPv4)");
    //			return NO;
    //		}
    //	}
    //	
    //	if (readStream6 && writeStream6)
    //	{
    //		r1 = CFReadStreamSetProperty(readStream6, kCFStreamNetworkServiceType, kCFStreamNetworkServiceTypeVoIP);
    //		r2 = CFWriteStreamSetProperty(writeStream6, kCFStreamNetworkServiceType, kCFStreamNetworkServiceTypeVoIP);
    //		
    //		if (!r1 || !r2)
    //		{
    //			LogError(@"Error setting voip type (IPv6)");
    //			return NO;
    //		}
    //	}
    //	
    //	return YES;
    
    // The above code will actually appear to work.
    // The methods will return YES, and everything will appear fine.
    // 
    // One tiny problem: the sockets will still get closed when the app gets backgrounded.
    // 
    // Apple does not officially support backgrounding UDP sockets.
    
    return NO;
}

#endif

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#pragma mark Class Methods
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

+ (NSString *)hostFromSockaddr4:(const struct sockaddr_in *)pSockaddr4
{
    char addrBuf[INET_ADDRSTRLEN];
    
    if (inet_ntop(AF_INET, &pSockaddr4->sin_addr, addrBuf, (socklen_t)sizeof(addrBuf)) == NULL)
    {
        addrBuf[0] = '\0';
    }
    
    return [NSString stringWithCString:addrBuf encoding:NSASCIIStringEncoding];
}

+ (NSString *)hostFromSockaddr6:(const struct sockaddr_in6 *)pSockaddr6
{
    char addrBuf[INET6_ADDRSTRLEN];
    
    if (inet_ntop(AF_INET6, &pSockaddr6->sin6_addr, addrBuf, (socklen_t)sizeof(addrBuf)) == NULL)
    {
        addrBuf[0] = '\0';
    }
    
    return [NSString stringWithCString:addrBuf encoding:NSASCIIStringEncoding];
}

+ (uint16_t)portFromSockaddr4:(const struct sockaddr_in *)pSockaddr4
{
    return ntohs(pSockaddr4->sin_port);
}

+ (uint16_t)portFromSockaddr6:(const struct sockaddr_in6 *)pSockaddr6
{
    return ntohs(pSockaddr6->sin6_port);
}

+ (NSString *)hostFromAddress:(NSData *)address
{
    NSString *host = nil;
    [self getHost:&host port:NULL family:NULL fromAddress:address];
    
    return host;
}

+ (uint16_t)portFromAddress:(NSData *)address
{
    uint16_t port = 0;
    [self getHost:NULL port:&port family:NULL fromAddress:address];
    
    return port;
}

+ (int)familyFromAddress:(NSData *)address
{
    int af = AF_UNSPEC;
    [self getHost:NULL port:NULL family:&af fromAddress:address];
    
    return af;
}

+ (BOOL)isIPv4Address:(NSData *)address
{
    int af = AF_UNSPEC;
    [self getHost:NULL port:NULL family:&af fromAddress:address];
    
    return (af == AF_INET);
}

+ (BOOL)isIPv6Address:(NSData *)address
{
    int af = AF_UNSPEC;
    [self getHost:NULL port:NULL family:&af fromAddress:address];
    
    return (af == AF_INET6);
}

+ (BOOL)getHost:(NSString **)hostPtr port:(uint16_t *)portPtr fromAddress:(NSData *)address
{
    return [self getHost:hostPtr port:portPtr family:NULL fromAddress:address];
}

+ (BOOL)getHost:(NSString **)hostPtr port:(uint16_t *)portPtr family:(int *)afPtr fromAddress:(NSData *)address
{
    if ([address length] >= sizeof(struct sockaddr))
    {
        const struct sockaddr *addrX = (const struct sockaddr *)[address bytes];
        
        if (addrX->sa_family == AF_INET)
        {
            if ([address length] >= sizeof(struct sockaddr_in))
            {
                const struct sockaddr_in *addr4 = (const struct sockaddr_in *)addrX;
                
                if (hostPtr) *hostPtr = [self hostFromSockaddr4:addr4];
                if (portPtr) *portPtr = [self portFromSockaddr4:addr4];
                if (afPtr)   *afPtr   = AF_INET;
                
                return YES;
            }
        }
        else if (addrX->sa_family == AF_INET6)
        {
            if ([address length] >= sizeof(struct sockaddr_in6))
            {
                const struct sockaddr_in6 *addr6 = (const struct sockaddr_in6 *)addrX;
                
                if (hostPtr) *hostPtr = [self hostFromSockaddr6:addr6];
                if (portPtr) *portPtr = [self portFromSockaddr6:addr6];
                if (afPtr)   *afPtr   = AF_INET6;
                
                return YES;
            }
        }
    }
    
    if (hostPtr) *hostPtr = nil;
    if (portPtr) *portPtr = 0;
    if (afPtr)   *afPtr   = AF_UNSPEC;
    
    return NO;
}

@end
